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THE 



WOWDERS 



OF THE 



HEAVENS, 



A POPULAR VIEW OF ASTRONOMY, 



INCLUDING A FULL ILLUSTRATION OF THE 



MECHANISM OF THE HEAVENS; 



EMBRACING THE 



SUN, MOON, AND STARS, 



WITH DESCRIPTIONS OF 



THE PLANETS, COMETS, FIXED STARS, DOUBLE STARS, THE CONSTELLATIONS, THE GALAXY, 

OR MILKY-WAY, THE ZODIACAL LIGHT, AURORA BOREALIS, OR NORTHERN 

LIGHTS, METEORS, CLOUDS, FALLING STARS, AEROLITES, &c. 



Xllustrateti ts Numerous fllapjs antJ SSnflrabinfls. 



BY DUNCAN BRADFORD. 

"The Heavens declare the glory of God." 




B OSTO'N: '^'^''" 

AMERICAN STATIONERS COMPANY 

JOHN B. RUSSELL. 

1837. 



Entered according to the Act of Congress, in the year 1837, by 
Samuel G. Goodrich, 
in tiie Clerks Office of the District Court of the District of Massuchusetts. 



CAMBRIDGE; 

FOtSOJI, WELLS, AND THURSTON, 

PRINTERS TO THK UNIVERSITY. 






PREFACE. 



In the preparation of this volume for the press, the main purpose, kept 
constantly in view, was to make the subject plain and interesting to the 
people. It has been heretofore too much kept from them, by the practice 
of mingling mathematics with it to such an extent as to alarm the neo- 
phyte at the very threshold of the temple of astronomy. 

To succeed in my attempt, I have judged it best to select, from such 
books as have fallen into my hands, those parts that were least encumbered 
with the abstruse and unintelligible, rather than to trust to my own powers 
of making a subject simple and attractive that is in itself almost too 
difficult for the majority of minds. How far I have succeeded, I must 
leave, not to the learned or the critic, but to the people themselves for 
whose perusal these pages are intended. 

The principal works used in the compilation were " Uranographie par 
Francoeur," "Manuel d' Astronomic par Bailly," "Astronomic Physique 
par Biot," "HerscheFs Astronomy," "Arago on Comets, translated by 
Farrar," Brewster's Ferguson," Silliman's Journal," Dick's Christian 
Philosopher," "Chalmer's Astronomical Discourses," "Forstei-'s Atmo- 
spheric Phenomena," ifec. From many of these I have largely drawn, and 
the least I can do is to make a general acknowledgment of the fact. 
Finally, I must rest my hopes of the success of this compilation, on the 
curiosity so natural to the human mind, that "awakes in us when free 
from cares a desire to learn what is going on even in the heavens." 

DuivcAJv Bradford. 



THE ENGLISH AND LATIN NAMES OF THE CONSTELLATIONS DESCRIBED 

IN THIS VOLUME. 



English Names. 


Latin Names. 


English Names. 


Latin Names. 


The Bull. 


Taurus. 


The Balance. 


Libra. 


Orion. 


Orion. 


The Serpent Bearer. 


Serpentarius vel Ophiucus. 


The Hare. 


Lepus. 


The Serpent. 


Serpens. 


Noah's Dove. 


Columba Noachi. 


The Northern Crown. 


Corona Borealis. 


The River Po. 


Eridanus. 


The Little Bear. 


Ursa Minor. 


The Charioteer. 


Auriga. 


The Scorpion. 


Scorpio. 


The Camelopard. 


Camclopardalis. 


Hercules. 


Hercules. 


The Lynx. 


Lynceus. 


Cerberus. 


Cerberus. 


The Twins. 


Gemini. 


The Dragon. 


Draco. 


The Little Dog. 


Ca7iis Minor. 


The Harp. 


Lyra. 


The Unicorn. 


Monoceros. 


The Archer. 


Sagittarius. 


The Great Dog. 


Canis Major. 


The Eagle. 


Aquila. 


The Ship Argo. 


Argo Navis. 


Antinous. 


. Antinous. 


The Crab. 


Cancer. 


The Dolphin. 


Delphinus. 


The Lion. 


Leo. 


The Swan. 


Cygnus. 


The Little Lion. 


Leo Minor. 


The Capricorn. 


Capricornus. 


The Sextant. 


Sextans. 


Andromeda. 


Andromeda. 


The Water Snake. 


Hydra. 


The Fishes. 


Pisces. 


The Cup. 


Crater. 


Cepheus. 


Cepheus. 


The Great Bear. , 


Ursa Major. 


Cassiopeia. 


Cassiopeia. 


Berenice's Hair. 


Coma Berenices. 


The Flying Horse. 


Pegasus. 


The Crow. 


Corvus. 


The Little Horse. 


Equulus vel Equi Seciio. 


The Virgin. 


Virgo. 


The Water Bearer. 


Aquarius. 


The Bear Driver, 


Bootes. 


The Southern Fish. 


Piscis Australis. 


The Greyhounds. 


Aster ion et Char a ^ vel 


Perseus. 


Perseus. 




Canes Venatici. 


The Head of Medusa. 


Caput Medusa. 


The Centaur. 


Centaurus. 


The Ram. 


Aries. 


The Cross. 


Crux. 


The Sea Monster. 


Cetus. 


The Wolf. 


Lupus. 







CONTENTS. 



CHAPTER I. 

Section I. — Appearances of the heaven — by day — by night — Diurnal mo- 
tion — Celestial sphere — Its poles— Zenith — Nadir — Sensible horizon — 
Rational horizon — Meridian — Equator — Hemispheres — East,-west, north 
and south points — Circumpolar stars— Declination and right ascension 
— Equality of a star's successive revolutions — how made known — Use 
of this regular motion to astronomers — Sidereal day — Time-keepers used 
by the ancients — Chronometers — Illustration of the preceding — Deduc- 
tions from appearances — Stars called Fixed — Idea of immensity im- 
pressed by the study of the stars — Annual parallax — Each star the 
centre of a system, and possibly the satellite of some more magnificent 
primary . 9 

Section II. — Division of the stars according to their apparent magnitudes 
— Their number infinite — Impartial distribution over the heavens — 
Milky way — Distance of the stars — Their probable dimensions and 
nature — Periodical stars — Temporary stars — Double stars — Their revo- 
lution round each other — Subject to the laws of gravity — Colored stars 
— Proper motion of the stars — Compound sidereal systems — Clusters — 
Nebute — Nebulous stars — Stars are visible in the day 16 

Section III. — Astronomy of the ancients — Their method of dividing the 
stars into constellations — Constellations easily distinguished — The divi- 
sion arbitrary, yet convenient — Anciently was important to the husband- 
man — Reason of the names of the constellations — The twelve signs of 
the zodiac — The origin of their hieroglyphic characters — Signs and 
constellations of the same name not coincident — Method of studying 
the stars — Fables, and descriptions of the constellations — ^Remarks — 
The heavenly bodies unequally distant from the earth — Earth compara- 
tively but an atom 31 



CHAPTER II. 

Section I. — Erroneous notions derived from appearances — Why the stars 
are not visible to the naked eye in the day-time — Fictions of poetry 
respecting the universe — Is the earth its centre ? — Does the earth rotate ? 
— Difierent constellations visible at different regions — Rotation of the 



earth consistent with appearances — Permanence of its axis — Precision 
of the ancients — Discovery by Copernicus — Causes of erroneous impres- 
sions — Consequences of considering the earth immovable — Centrifugal 
and centripetal forces — Pendulum a means of finding the force of attrac- 
tion — Measures of gravity — Attraction not a simple force — Effects of 
the earth's rotation — Trade winds — Proofs of wisdom in the rotation of 
the earth — Consequences of a changeable axis — Advantages ■ of the 
existing law of attraction — Perturbations periodical 56 

Section II. — -Sun's apparent motion — Ecliptic — Celestial latitude and lon- 
gitude — Tropics — Does the sun really move in the ecliptic ? — Impulse 
requisite to produce the motions of the earth — Appearance of the mo- 
tions of the planets as seen from the sun — System of Tycho Br3,he — 
Proofs of the earth's double motion — Annual parallax — Axis of the 
earth always points to the same celestial poles — Its inclination to the 
ecliptic — Radius vector — Cause of the change of seasons — Zones — 
"Winter at the poles — Illustration of the foregoing — Nature of the earth's 
orbit — Poetical rising and setting of the stars — Perihelion and aphelion 
— Designing wisdom apparent from the figure of the earth's orbit. 69 

Section III. — The horizon and its dip — The earth at first supposed a lim- 
ited plane — Early reasoning to the contrary — Proof furnished by na,vi- 
gation — Objections caused by our ideas of weight — Answered — Conical 
figure of the earth's shadow — Other proofs — Different aspects of the 
heaven according to the position of the observer — Time difierent in 
different places at the same absolute instant — Method of measuring an 
arc of the meridian — The earth an oblate spheroid — First meridian — 
Original constitution of the earth — Extent of the horizon proportioned to 
the height of the eye — Visible portion of the earth's surface — Tempera- 
ture of the earth at its surface — Internal heat — Atmosphere — Reflections 
on the wisdom and knowledge of the Creator — Diversities of the 
globe 82 

CHAPTER III. 

Section 1. — Sun — Comparatively stationary — Cause of twilight — Sun's 
mass — Gravity — Real diameter — Probable conclusions of the solar as- 
tronomer — Sun's disc as seen from the different planets — Sun the source 



VI 



CONTENTS. 



of heat — What proportion of solar light falls on our globe — Divine 
wisdom — Solar spots — ^Variable in size and number — First authentic 
observations on — -Scheiner imagines they are planets — Their course 
and changes — Sun's revolution about its axis — Theories of different 
observers respecting the spots — Herschel's theory prevalent — Is the sun 
inhabited ? — Zodiacal light — Sun's progressive motion — Herschel's theo- 
ry confirmed by a late experiment in France 99 



CHAPTER IV. 

Section I. — Hori2ontal moon — An illusion — Mode of estimating distances 
— Variation of the moon's distance from the earth — Motion from west 
to east — Amount of motion per day — Per minute — Moon's nodes — 
Syzygies — Lunar Cycle — Golden number — The moon's periodic, synodic 
and sidereal revolution — Disturbance of the moon's orbit. . . . 119 

Section II. — Phases of the moon^Law of their variation — The new hold- 
ing the old moon — Earthshine — Earth new when the moon is old, and 
vice versa — Proportion of moonlight at different seasons and places — 
Harvest-moon — Libration in latitude — In longitude — Diurnal — Lunar 
mountains — Atmosphere 124 

Section III. — Recurrence to the phenomenon called the new holding the 
old moon — Moon supposed by some to be phosphorescent — Leslie's ex- 
planation of the thread of light connecting the horns of the new moon — 
True explanation — Surface viewed through a telescope — Mountains and 
hollows — Lunar volcanoes — Arguments respecting the atmosphere — Is 
the moon inhabited? — Discovery of a fortification and of roads in the 
moon 138 



CHAPTER V. 

Section I. — The system of the world — Limits of magnitude and minute- 
ness — Theories respecting the world — Ptolemy's — Egyptian — Tycho 
Brahe's — Copernican — Des Cartes' whirlpools — Number and names of 
the planets — Origin of their symbols — Their comparative distances from 
the sun — Their division into inferior and superior — Their periodical 
times — Their secondaries — Origin of the planet's names — Heliocentric 
circle of a planet — Aspects, what — Venus both an evening and a morning 
star — Its phases — Why imperceptible to the naked eye — Inferior planets 
— Their geocentric motions in looped curves — Mars — The form of its 
disc — lis orbit without the earth's— Aspects and motions of superior 
planets — Mode of determining the position of the orbits — Elements of 
an orbit — Predicting a planet's return to the same situation — Venus 
sometimes visible at noonday 146 

Section II. — Individual planets — Mercury — Period of its revolution — 
Method of finding its rotation — Motion in its orbit per hour — When 
visible— Its diameter and distance from the sun — Its telescopic appear- 
ances — Its mountains — Its atmo.sphere — Venus — Its distance from the 



sun, diameter, and rate of motion — Its period— Inclination of its orbit — 
Telescopic appearances — Atmosphere — Rotation— Mountains— Mars — 
How the earth and moon appear there— Its irregularities the subject of 
Kepler's studies — Peculiarities in its appearance — Effects of its atmo- 
sphere on the color of the planet — Its luminous zone, and the cause of 
the same— Mars supposed phosphorescent — Ultra zodiacal planets — 
Seemingly disturb the harmony of the system — Their feeble powers of 
gravitation — Peculiarities of Ceres— of Pallas — of Juno — of Vesta — 
Giber's theory respecting the small planets. 165 

Section III. — Jupiter's form — Its situation — Length of its year — Rapidity 
of rotation— Small change in its seasons^Alternately morning and 
evening star — Its belts — Degree of oblateness — Cause of the belts — 
Jupiter's satellites — Particulars respecting them — Velocity of light — 
Saturn's size compared with the earth's — Surrounded by a ring — Singu- 
lar form of Saturn — Its spots and belts — Why this planet is more oblate 
than Jupiter — Saturn's satellites — Position of their orbits — Theories 
concerning the rings — Their different appearances — Their revolution — 
How they are sustained — Herschel, particulars of — Its satellites — Their 
peculiarities — How kept in their orbits 175 



CHAPTER VI. 

Section I. — Comets — Little known of their nature or purposes — Their 
number — Comet of 1680 — The tail not an invariable appendage — What 
are the essentials of a comet — How distinguished from a planet — An- 
ciently considered as meteors — Proof to the contrary — Elements of a 
cometary orbit— Motions of a comet — How recognised — Halley's comet 
— Lexell's— Encke's — Biela's — Do comets affect the temperature of our 
seasons ? — Physical constitution — The envelope — Nucleus — Tail — Do 
comets have phases ? — Variation in the size of the envelope. . . 189 

Section II — Chances against a comet's striking the earth — Do they finally 
fall into the sun? — Or into the stars? — Can the earth draw off the tail 
of a comet? — The effects — Were the fogs of 1783 and 1831 caused by a 
comet? — Was the cholera caused by a comet? — The deluge not caused 
by a comet— Has the climate of Siberia suddenly changed— Is the 
severe climate of North America owing to a comet ? — Is the depres- 
sion in the centre of Asia owing to a comet? — Was the moon ever a 
comet? 207 



CHAPTER VII. 

Section I. — Reflections on the system — Proofs from analogy that the plan- 
ets are inhabited — Their magnitude — Their rotation — Their revolution 
round the sun — They have moons — Blountains and valleys— Clouds 
and snow — Our globe a small part of the universe— No limits to future 
discoveries — Rapid motion of the planets — Infinite power requisite to 
give them this motion — Immense spaces around the heavenly bodies — 
Their mutual influences — Astronomy an aid to religion. . . . 217 



CONTENTS. 



Vll 



CHAPTER VIII. 

Section I. — Eclipses — All opaque bodies cast shadows — The moon visible 
during total eclipses — Explanation of this phenomenon — Lunar eclipses 
universal — The shadow conical — The penumbra, or partial shadow — 
Eclipses of the sun not universal — Breadth of the lunar shadow on the 
earth — Primaries never eclipse each other — Duration of total eclipses — 
Solar and lunar ecliptic limits— Detail of several eclipses— Eclipse of 
585 B. C— of 434 B. C— of 383 B. C— of 201 B. C— Two mentioned 
by Dionysius — Chinese customs respecting eclipses — Eclipse of 1560 — 
of May, 1706— of April, 1715— of June, 1406— Annular eclipse of 1836 
—Number of eclipses in a year— Particular explanation of eclipses- 
How affected by the position of the earth's axis— Use of eclipses in 
astronomy, geography, and chronology— Darkness at the crucifixion— 
Occultations. 224 

Section II. — Universal gravitation — Dr. Hooke's suggestions and experi- 
ments Newton's successful investigation — All bodies tend toward each 

other— Pressure and weight the effects of gravity— Heavy and light, 
relative terms — Weight varies at different parts of the earth — How dis- 
covered — Gravity diminishes as we recede from the centre — There 
would be no weight if but one body existed — Gravity retains the moon 
in its orbit — Explanation — The planets affected by the same force — 
Natureof this force inexplicable-^Attraction of mountains. . . 243 

Section III. — Tides — Kepler's fanciful theory — Newton's theory — General 
course of the tides — Owing principally to the moon's attraction — In part 
to the sun's — Farther explanation of the tides^Cause of spring and 
neap tides — Priming and lagging of the tides — Declination of the sun 
and moon affect the tides— Establishment of a port— Exceptions to the 
general laws— Mediterranean and Baltic seas — Times of high water 
different in neighboring ports— Theory of Mr. Redfield. . . . 250 

Section IV.— Solar and sidereal days — Equation of time — Inequality 
arising from the obliquity of the ecliptic — That caused by the unequal 
motion of the earth in its orbit — Deductions respecting the equation 
throughout the year — Mean and apparent time agree but four days in 
the year — Calendar — Standards of time — Their inconvenience — Grego- 
rian method of correcting the calendar — Grecian calendar — Eoman 
Calendar — Its correction by Julius Cssar — Persian calendar — Subdivi- 
sions of the year — Cycle — Dionysian period — Dominical letters — Julian 
period. 259 



CHAPTER IX. 

Section I. — Mensuration of the earth — Standard of measure — Astronomy 
teaches how to obtain the dimensions of the globe — Richer's observations 
on the pendulum — Their consequences — Laws of the pendulum — Oblate 
form of the earth confirmed by analogy — Early attempts to measure the 
earth — Riccioli's method — Snellius — Norwood — and others — Opposite 
theories of Newton and Huygens — Maupertuis measures a degree in 



Sweden, and Godin in Peru— Result— Explanation of the method of 
measuring the earth 275 

Section II. — Methods of finding the moon's parallax and distance — DiiR- 
culty in finding the sun's parallax — Transits of Mercury and Venus — 
Sun's parallax found by the transit of Venus.— The sun's distance — 
Distances of the planets — Method of finding the diameters and magni- 
tudes of the sun and planets — Method of finding their masses and den- 
sities 281 

Section III. — Nature of light unsettled — Its properties known — Refraction 
— Experiments illustrating refraction — Cause of twilight — Advantages 
and disadvantages of refraction— Knowledge of the atmosphere impor- 
tant to the astronomer — Amount of refraction at the zenith, the horizon, 
and at intermediate points — Explanation of the " sun drawing water" 
— Terrestrial refraction — Aberration — Bradley's observations — Infer- 
ences — Motion of light — Aberration confirms the motion of the earth in 
an orbit — Precession of the equinoxes — Nutation — Obliquity of the 
ecliptic — Its cause and effects 287 

Section IV. — The telescope — Its invention — Its simplest form — Mode of 
finding the magnifying power of telescopes — Common astronomical 
telescopes — Difficulties encountered in their early construction — Huy- 
gens' improvement — Newton's lenses — Reflecting telescopes — The New- 
tonian — The Gregorian — The Cassegrainian — W. Herschel's — Ramage's 
— General remarks on telescopes — Impossibility of minute discoveries 
in the moon 300 



CHAPTER X. 

Section I. — Zodiacal light — Observed by Cassini in 1683 — By Childrey 
previous to 1661 — By others in 1707 — By Professor Olmsted in 1834 — 
Various theories — Aurora borealis — Appearances in the Shetland Isl- 
ands — In Siberia — At Hudson's Bay — Sounds attending their appear- 
ance — Aurora seen by Capt. Ross — Southern lights observed by Forster 
— Northern lights as seen in England, March, 1716 — Supposed height 
of these meteors — Theories respecting their cause — Halley's — Mairan's 
— Euler's — Franklin's — Kirwan's — Appearances in August and Sep- 
tember, 1827— December and November, 1835— April, 1836. . . 309 

Section II. — Remarkable halos and parhelia seen in France in April, 1666 
— In March, 1667 — Huygens' explanation of the causes of such phe- 
nomena — Mariotte's explanation of halos — Mock-moon seen by Forster — 
Extraordinary circles round the moon seen at New Haven in November, 
1827 — Phenomenon seen at Green Bay in February, 1835 — Experiments 
illustrating the production of halos — Rainbows — Experiments producing 
colored bows — Cause of rainbows — Remarkable bows observed by Brew- 
ster— At Chartres— By Halley— In 1710— In July, 1824— Clouds— Their 
modifications — Curl-cloud — Stacken-cloud — Fall-cloud — Sonder-cloud — 
"Wane-cloud — Twain-cloud — Rain-cloud — Scud — The color of clouds — 
Their height — Their structure and buoyancy 327 



vm 



CONTENTS 



Section III. — Division of falling meteors — Phenomenon witnessed at 
Leeds, England, 1710— In March, 1719, aU over England— In March, 
1813, at New Haven, Connecticut — In Vermont, January, 1817, and 
March, 1822 — In various places, November 13th, 1833 — Olmsted's theo- 
ry respecting its cause — Repetition of the meteoric phenomenon in 1834, 
1835, 1836 — Arago's theory — Ignes fatui, or Will-o'-the-wisps. . . 348 



Section IV. — Aerolites — Their resemblance to each other — A proof of 
their common origin — Direction in which they appear to move — No 
theory as to their origin satisfactory — Accounts of various aerolites — 
Their specific gravity— The substances of which they consist — They 
could not have been produced in the atmosphere — Do they fall from the 
moon ?— Or, are they fragments of an exploded planet ? . . . . 362 



WONDERS OF THE HEAVENS. 



CHAPTER I. 



SECTION I. 

Appearances of the heaven — ^by day— by night — Diurnal motion — 
Celestial sphere — Its poles — Zenith — Nadir — Sensible horizon 
— Rational horizon — Meridian — Equator — Hemispheres — East, 
west, north and south points — Circumpolar stars — Declination 
and right ascension — Equality of a star's successive revolutions — 
hffw made known — Use of this regular motion to astronomers — 
Sidereal day — Time-keepers used by the ancients — Chronometers 
— Illustration of the preceding — Deductions from appearances — 
Stars called Fixed — Idea of immensity impressed by the study of 
the stars — Annual parallax — Each star the centre of a system, and 
possibly the satellite of some more magnificent primary. 

Take a man who had been blind from his birth, 
and who had imbibed no ideas of any existences but 
those that were immediately and intimately con- 
nected with his other senses, restore him suddenly 
to perfect and healthy vision, and place him in 
some extensive champaign, where there were no 
obstacles to confine his view ; would he not dis- 
cover a scene the most brilliantly beautiful mortal 
eye ever beheld ? That azure dome sown broad- 
cast, as it were, with living light ! How would he 
desire to understand the causes of the changes he 
would witness, the regular and constant succession 
of day and night; phenomena so different, yet each 
so interesting to his new-born and startled sense. 
Soon after the dawn of day, he would observe in 
one part of heaven a dazzling circle rising appa- 
rently out of the earth, and scattering about it in 
all directions numberless rays of brilliant light. It 
ascends slowly the gorgeous dome, the heat and 
light increasing as it ascends, until it attains a 
point nearly overhead, where it seemingly rests 
but a moment in its midway course, then descends 
as it arose, and disappears at last in a part of the 
horizon opposite to that where it first appeared. 



The light soon fades away, and night comes on, 
bringing a new and more interesting, if not so 
brilliant a spectacle. During the day, a single 
body had attracted all admiration to himself, by 
his majestic motion and the splendor of his rays. 
Now there appear on all sides shining points, vari- 
able in size and brightness, decorating in countless 
numbers the vault of heaven, and increasing still 
in proportion as the darkness becomes more pro- 
found, till the whole celestial space seems to be 
filled. The motion of these bodies adds also to 
the beauty and interest of the scene. Some, moving 
in the same direction as the sun, disappear like 
him from our view in the west. Others are rising 
in or near the east, and ascending in their turn. 
Such are the general phenomena of the rising and 
setting of the heavenly bodies. Yet all do not 
thus disappear below the horizon. There are some 
which never reach that circle, and whose track can 
be followed during the whole night. Those stars 
which form the cluster called the Great Bear, or 
Charles' Wain, are among this number in our lati- 
tude ; and if one stations himself with his right 
hand toward the east and his left toward the west, 
he will see this group, so well known in our cli- 
mate, assume successively different positions, while 
the individual stars of the group maintain the same 
mutual relations of figure and distance. Meantime 
the darkness diminishes, the dawn reappears, the 
light increases, the sun by his superior brightness 
dims the light of the stars, and the phenomena of 
morning are renewed in the same order as before. 
This general movement of the heavenly bodies 
from east to west, in the course of a day and night, 
is called the diurnal motion. In what we have said 



10 



WONDERS OF THE HEAVENS. 



above, we have brought forward only those phe- 
nomena, which appear on a simple inspection. 

The different motions that we have observed in 
the heavens may have led us to think that we were 
situated in a point of the universe, around which as 
a centre revolves a sphere sprinkled with shining 
drops. This sphere seems to turn on an imaginary 
line, which is called the axis of the earth, the points 
where this line touches the heaven being the celes- 
tial poles; the one that is elevated in our latitude 
being called the northern or Arctic pole, and that 
which is diametrically opposite, and which we can- 
not perceive, the southern or Antarctic pole. We 
must be careful not to confound these two points 
with that situated directly over our head and its 
opposite, the first of which is the zenith, the last 
the nadir. Every point on the surface of the earth 
has its zenith and its nadir; yet there are but two 
points whose zeniths coincide with the poles of the 
heaven, and these are the poles of the earth. Thus, 
let be the place of the observer, P and P' the 




poles of the heaven, p and p' the poles of the 
earth; Z is the zenith and N the nadir of the ob- 
server at 0. If the observer were at e, his zenith 
would be E and his nadir E'. 

If now a plane, A B, be imagined tangent to the 
surface of the earth at 0, it will represent the sensi- 
ble horizon of a spectator at that point, separating 
the parts of the heaven and earth visible, from the 
parts invisible to him. There is another horizon, 



called the rational. It is a plane, parallel to the 
sensible, and passes through the centre of the 
earth, which is also the centre of this circular 
plane; thus H H' represents the rational horizon of 
the observer at 0, Everyplace, then, must have a 
sensible and rational horizon peculiar to itself. 
These planes are quite important in astronomy. 
From them we measure the altitude of the heaven- 
ly bodies ; and these measures are the foundation 
of astronomy. 

The great circle which passes through the poles 
of heaven and the zenith of a place is the meridian 
(north and south line) of that place. 

The stars, supposed fixed to this celestial sphere, 
describe every day circles, smaller according as 
they are situated nearer the poles of the heaven. 
The largest of these circles, whose points are all 
equally distant from the poles, is called the equator, 
while the circles parallel to it are called simply 
parallels. The equator divides the sphere into 
two equal parts; one forms the northern, the other 
the southern hemisphere. 

The east is that point in which a heavenly body 
(describing the equator) rises; the west, the point 
where the same body sets. The intersection of 
the horizon by the meridian determines two other 
points ; the south, where the sun is at noon in 
regard to us, and the north, where the sun is at 
noon in regard to those situated as far south, as we 
are north of the equator. These four points are 
known under the name of the cardinal points. 

If we have observed the movements of the vari- 
ous stars, we must have noticed, that some of them 
never set, but are constantly above the horizon. 
Among these, a few experience but a very slight 
displacement, and scarcely appear to move at all. 
These, being near the axis about which all the 
heavenly bodies revolve, describe diurnal circles of 
so small a diameter, that they are scarcely discerni- 
ble by the eye. Yet during their revolution they 
are seen to pass the meridian twice, once over the 
upper meridian, that is, between the pole and the 
zenith, and once over the lower meridian, that is, 
between the pole and the horizon. These heavenly 
bodies are denominated circumpolar. 



WONDERS OF THE HEAVENS 



11 



The situation of the stars in reference to the 
equator is given by stating their declination and 
right ascension. The declination of a star is its 
distance from the equator measured on the arc of 
a great circle which passes through its centre and 
through the celestial poles, and is analogous to ter- 
restial latitude, being north or south as the star is in 
the one or the other hemisphere. -Right ascension 
is the distance of a heavenly body from an arbitrary 
first meridian, (that which passes through the first 
point of Aries,) and is measured on an arc of the 
celestial equator, being analogous to celestial lon- 
gitude, except that it is measured in one direction 
only, quite round the sphere. 

Of all the phenomena which the diurnal motion 
of the stars presents, that, which has most fixed the 
attention of observers, is the constant equality of 
every revolution of the same star. If we direct a 
telescope toward any star, fix the instrument firm 
and immovable, and observe the time which passes 
until it again appears in the instrument, we may 
feel assured that we have the time of its revolution 
for all duration, as also that of every other star. 
At most, the variations are so small, as to be appre- 
ciable only in some stars near the axis of rotation. 
Astronomers make use of them to obtain with pre- 
cision a measure of time. The interval between 
two consecutive returns of a star to the same meri- 
dian is styled a sidereal day. The instruments 
first used to measure this duration, called clepsy- 
dras, vessels filled with water, sand, or mercury, 
and used like our hour-glasses, were exceedingly 
rude and inexact. In later times, new discoveries in 
physics, and more ingenious mechanical skill, have 
caused the manufacture of nicer time-keepers, such 
as watches and clocks; and in later still, the chro- 
nometer, whose degree of exactness almost exceeds 
belief, since some of them have been said to vary 
less than one second per diem. 

After having observed the times of the revolution 
of the stars, a very simple question presents itself 
to the mind; — Is the sidereal motion uniform? does 
a star pass over equal spaces in equal times? This 
is found to be the case. It follows therefore that 
to state how much a star has been displaced, it is 



indifferent whether we mention the number of de- 
grees in the arc passed over, or the interval of 
time taken up in the passage, provided it has al- 
ready been determined how many degrees it passes 
over in any given time. Since the heaven per- 
forms its revolution in twenty-four hours with an 
equable motion, if we divide all the diurnal circles 
into three hundred and sixty degrees, every degree 
into sixty minutes, and every minute into sixty 
seconds ; the stars will describe arcs of fifteen 
degrees every hour, of one degree every four 
minutes, and of a minute in every four seconds of 
time. But an important distinction between the 
different circles is to be borne in mind; viz., that 
the parallels being small circles, their degrees, 
minutes and seconds will not be of the same abso- 
lute length as those of the great circles ; therefore, 
to compare the results, we must first determine the 
value of a degree on each parallel as compared 
with that of a great circle. That the motion of the 
stars is constantly uniform, that it is exactly circu- 
lar, and that it is made round the same axis, has 
long been beyond a doubt in the minds of astrono- 
mers. 

Let H R N T represent the horizon of an ob- 
server; 0, (the centre of that circle and of the 




T ... t 






p- 



hemisphere H Q, j N,) being his position. Let T 
be the spot where a star first rises, T Q, R its path 
above the horizon, and R the point where it sets; 
and let the arc T H R of the horizon, intercepted 
in one direction between the points T, R, be bi- 
sected in the point H, and the arc T N R, inter- 



12 



WONDERS OF THE HEAVENS 



cepted in the other direction, be bisected in the 
point N, It is clear that H and N are at the two 
extremities of a diameter, for H E. is equal to H T, 
and R N is equal to N T, and therefore, H R N 
(the sum of H R and R N) is equal to H T N (the 
sum of H T and T N;) or H R N, H T N are each 
of them semicircles. Now, suppose t q r to be 
the path of another star above the horizon, t its 
point of rising, r its point of setting ; it will be 
found that the arc i H is equal to the arc H r, 
and ^ N is equal to N r; that is to say, the points 
N and H in this case also bisect the arcs of the 
horizon intercepted between the points of rising 
and setting. The same will be found to be true of 
every star, (with some apparent exceptions, to be 
presently noticed,) and the points N and H are 
consequently fixed points, and independent of the 
particular stars, by observation of which they were 
ascertained. Let H Q ^ N be the intersection 
with the celestial sphere of the plane passing 
through N H and perpendicular to the horizon; 
this is the meridian of the observer at 0, and as 
the points N and H are fia:ed, the vertical plane 
drawn through them must be fixed also ; this 
meridian therefore is a fixed line. It will also be 
found by observation, that the points Q, q, where 
the paths of the different stars meet this meridian, 
are the most elevated points of those paths respec- 
tively, and consequently that a star which rises 
and sets attains its greatest height above the hori- 
zon, or culminates, when it is upon the meridian; 
and we may add, that the paths, T Q, R, if ^ r, of 
the stars observed, appear to be parallel to each 
other, and that each path is divided by the meri- 
dian into parts T Q, Q, R, or ^ ^, 5- r, apparently 
equal and similar; that is to say, T Q equal and 
similar to Q, R, and t q to q r. 

In one part of the heavens the appearances are 
a little different. If we look to the northern part 
we shall see many stars, which never sink below 
the horizon. These stars pass the meridian twice, 
once at the lowest, and once at the highest point 
of their course. In moving from the lowest to the 
highest point, their course is entirely to the east 
of the meridian; in passing from the highest to the 



lowest point, it is entirely to the west of that line. 
These parts also in this case, as well as in that al- 
ready mentioned, are similar and equal; and if the 
course of one of those stars be represented in the 
figure by the line U X V Y, every point in that 
line will be found to be equidistant from a certain 
point P, situated in the sphere, and U X V Y will 
be a circle, and the point P its pole. Besides this, 
it will be found that the path of every one of these 
stars which never set is a circle described at a 
given distance from the same point P, which itself 
appears stationary; and the position of this point 
being ascertained, it will further be found, that 
each of the paths T QR, t q r, described by stars 
which alternately rise above the horizon and fall 
below it, and which appear, as we have already 
mentioned, to be parallel to each other, are them- 
selves also portions of circles, every point of which 
is equidistant from the same point P, and which 
therefore are parallel to each other, and to the 
path U X V Y, described by a star which never 
sinks below the horizon. The point P therefore is 
the pole of all the parallel circles described by the 
stars; and if we suppose the sphere to be complet- 
ed, as it is by the dotted lines in the figure, and p 
to be the point directly opposite to P, p will be the 
other pole of the same circles; or there are two 
fixed points, one P found by observation, the other 
p deduced from it, to which the motion of the stars 
may be equally referred. 0, being the centre of 
the sphere, will be a point in the line which joins 
P, p. We shall also find, that in the time in which 
any particular star describes a third or fourth part, 
or any given portion of its circle, all others de- 
scribe the same portion of theirs; and consequent- 
ly they all continue in the same positions with 
respect to each other, though their places vary 
with respect to the horizon and the observer. 

Having thus far ascertained the appearances 
which the stars present, let us see if we can thence 
deduce any conclusions respecting the occasion of 
them. For this purpose let us suppose the hemi- 
sphere, H Q, P N, to be made a complete sphere, as 
is done by the dotted lines in the figure. Let us 
also suppose that the whole sphere has a motion of 



WONDERS OF THE HEAVENS 



13 



rotation round a line joining P,/), but that H R N T, 
the horizon, or the line in which the plane bound- 
ing the visible hemisphere meets the heavens, con- 
tinues fixed : and let us see vv^hat would be the 
appearances presented in such a case. Let us take 
the case of a star upon the horizon at T, It is 
clear that, as by the rotation of the sphere it was 
transferred from T, it would appear to move in a 
line of which every point was equidistant from P, 
for every point in that line would be determined 
by the actual distance of the star from P. Its ap- 
parent path therefore would be a portion of a cir- 
cle, every point of which is equidistant from P; 
and, in point of fact, we have already seen that it 
is so. In the same manner, if there be a star 
which never falls below the horizon, and whose 
distance from P is P V, its apparent path would be 
a circle, of which every point is at the same dis- 
tance P V from P ; or it would be represented by a 
circle, U. X V Y, which we have already seen to 
represent the apparent path of a star which never 
sets. Each of these circles, thus described by the 
motion of different stars, having every point in it 
equidistant from the same point P, they all would, 
as before, be parallel circles. Again, as each of 
them is described in consequence of the same gene- 
ral motion of rotation of the whole sphere, each 
would be described in the same time; namely, the 
time of that rotation; and in the same manner, in 
any portion of that time, each star would describe 
the same portion of its own circle ; namely, the 
same portion of that circle which the sphere de- 
scribes of a complete revolution. All these are 
the appearances which we have already seen that 
the heavens, in fact, present. 

The appearances presented by the motions of the 
stars may then be accounted for on the supposition 
that the sphere of the heavens revolves round an 
axis joining P, p. They cannot be explained how- 
ever on this supposition, except by supposing that 
the sphere goes through a complete revolution. 
The motion of a star which is seen to rise and set, 
as that whose path is T Q R, might be explained 
by imagining the sphere to make only a part of a 
revolution; and the magnitude of that part would 



depend on the proportion which the visible path 
T Q, R bore to the whole circle of which it formed a 
part; but the stars which never set, as that whose 
path is U X V Y, are seen to describe the whole 
circle, and their motion therefore can only be thus 
explained on the supposition of a complete revolu- 
tion of the heavens on the axis P p. If however 
this be the case, the motions of the stars which 
sink below the horizon must also be continued be- 
low it ; or they will describe below it the remaining 
parts (those represented by the dotted lines) of the 
circles T Q R B, tqrb. Let us see if we have any 
means of discovering, by observation or reasoning, 
whether they do so. 

The first remark, that occurs on this question, is, 
that the supposition, that they describe below the 
horizon the remainder of the circle, of which they 
are seen to describe part above it, at once accounts 
for one circumstance that seems to admit of no 
other explanation. We trace the path of a star 
from its rising at T, to its setting at R, and then 
lose sight of it; but on the next night we again see 
it appear at the same point, T. We know there- 
fore that the star is in some way transferred from 
the point R, where it sets, to the point T, where it 
rises; and the most probable way, in which we can 
suppose this transference effected, is by the continu- 
ation below the horizon of the same motion which 
it had when above it, or by the description of that 
circle, R B T, which it would describe on the sup- 
position that the whole heavens revolve round the 
observer. • 

If however we take the case of a star rising just 
at the time when the stars begui to appear in the 
evening, and setting as day breaks on the following 
morning, it is evident that its path below the hori- 
zon, if it be described at all, must be described by 
day; or that the same motion of revolution con- 
tinues by day, which we seem to have ascertained 
to exist by night. Does observation then confirm, 
or disprove this conclusion? The sun and moon 
are visible by day, but their motions, although they 
generally confirm it, are of a more complicated 
nature, and we therefore do not wish to draw our 
inferences on this point from them; and the stars 



14 



WONDERS OF THE HEAVENS 






are not visible to the unassisted eye when the sun 
is above the horizon. The telescope, however, in 
the hands of a skilful observer, for only such a one 
can make the observations necessary for this pur- 
pose, removes this difficulty; with it he can, even 
when the day is brightest, ascertain the positions 
from time to time, and consequently the motions, 
of many of the brighter stars ; and the result of 
these observations, is, that the stars are ascertained 
to describe in the daytime the same courses which 
they are easily seen to trace in the night : and we 
consequently come to the conclusion that their mo- 
tions may be accurately comprehended and explain- 
ed, on the supposition that the whole heavens re- 
volve about an axis, passing through the position 
of the observer, and carry the particular stars with 
them in their revolution. 

If this be so, and the meridian of the place, 
H Q, P N, be continued, as by the dotted line N Bp H, 
below the horizon, so as to complete the circle, this 
lower part of the circle will again intersect the 
circles T Q, R B, tqrb, in the opposite points, B, b, 
to those, Q, q, where the upper part of it met them 
above the horizon; and as Q, q, were the points 
must elevated above the horizon; B, b, will be those 
most depressed below it; or in other words, every 
heavenly body, which sinks below the horizon of a 
particular place, will be most depressed below it, 
when it passes the meridian of that place below the 
horizon, and of course below the pole. We have 
already seen a corresponding result with respect 
to circumpolar stars, when they cross the meridian 
below the pole though above the horizon. 

As yet we have only considered the conclusions 
which an observer, confined to a single point on the 
earth's surface, would arrive at on this subject. We 
will now proceed to examine, how they will be af- 
fected by a comparison with the results of other 
observations, made at a different place. The ac- 
count which we have given of the observations 
made at one place, applies with equal correctness 
to all; that is to say, an observer situated any- 
where upon the earth, finds that the apparent paths 
of the stars are circles, or portions of circles, each 
having every point in it equidistant from two fixed 



points, one in the observed heavens, and one in the 
other part of the sphere, supposed to be completed, 
and each bisected by a line passing through the 
visible fixed point, and dividing the visible heavens 
into two equal portions. In each case therefore, 
this line is what we have termed the meridian of 
the place of observation; and every place therefore 
has a meridian, passing through a fixed and im- 
movable point in the heavens. The position of 
this point may be ascertained by observation at 
each particular place, and it is found to be the same 
at all places; the other extremity of the axis also 
is the same in every place. 

We come therefore to this conclusion, that the 
axis P p round which the revolution of the heavens 
takes place is a fixed and determined line, not 
depending on the situation of the observer: and this 
is one circumstance necessary to the establishment 
of our theory, that the apparent motions of the stars 
may be attributed to the revolution of the heavens 
round a fixed axis; for if observations made at each 
place gave a different axis, they would be inconsis- 
tent with such a supposition. The points P, p, are 
only imaginary points, being those where the axis 
Pj9 meets the imaginary sphere of the heavens; 
they are however important to be known, and go 
by the name of the poles of the heavens. They are 
points, as we have already seen, in the meridian of 
every place, and therefore they no where appear 
either in the east or west side of the heavens: if 
however we conceive the heavens divided by a verti- 
cal plane, passing through the east and west points 
at any place, the points P and p will always be 
on opposite sides of this plane ; that is to say, the 
one on the north side of it, the other on the south, 
and the same point P is always on the same side of 
the place. If therefore {in fig- !•) P represent the 
pole, which to an observer at 0, is on the northern 
side of the heavens, P is always on the northern 
side, and is called on this account the north pole 
of the heavens ; and in like manner P' is the south 
pole. There are however two points on the earth, 
(the poles of the earth,) where the points P, P', are 
the one directly over the head, the other directly 
under the feet of the observer; here therefore there 



WONDERS OF THE HEAVENS 



15 



is no north or south point, and we shall hereafter 
see that the phenomena from which we deduced our 
definition of these points, namely, the rising and 
setting of stars, do not take place at these situa- 
tions. We have already seen that P, p, are points 
in the meridian of every place; all these meridians 
therefore intersect each other at the two poles. If 
p, the south pole, be above the horizon, P, the 
north pole, will of course be below it. 

One circumstance may here require explanation 
before we proceed farther. We have already seen 
that the centre of the heavenly sphere is a point in 
the axis P p, and that this centre appears to be the 
situation of the observer; and we have also said 
that the results of observation are the same, where- 
ever on the earth's surface he be placed. If two 
observers be at situations, the one, one thousand 
miles east of the other, the situation of both cannot 
be in the line V p; but if the one is in it, the other 
must be nearly one thousand miles out of it: yet 
they both appear to be in it. We know from very 
simple reasoning, or we may easily satisfy ourselves 
by trial, that a small change of position in the ob- 
server does not affect the apparent position of a 
very distant object. Thus, if there be two trees, 
or two spires, distant ten miles from each other, and 
two men stand half-way between them, the one 
precisely in the line joining them, and the other a 
yard on one side of it, each will alike feel that, to 
all common observation, he is exactly in the line 
which unites them. The angle between the two 
directions, in this case, would be considerably less 
than half a minute, and would not be observable 
except by instruments of some delicacy. In the 
same manner, if the distance to the points P, p, be 
excessively great in proportion to the distance 
between the situations of different observers, each 
observer will seem to be in the same position with 
respect to the points P, p, and the line joining 
them. There is therefore nothing absurd or con- 
tradictory in the apparent coincidence of each 
situation with the line P^, if we only suppose the 
points P, p, so remote from the earth, that any line 
drawn on its surface is too small to be estimated in 
comparison with that distance ; and we get there- 



fore a notion of the vast distance of those points, 
instead of a difficulty affecting the notion of such a 
revolution as we have supposed to take place. If 
however every point on the earth's surface be 
apparently in the line V p, so must its centre be 
also, which lies in the midst between these points. 
The axis P p therefore may be considered to pass 
through the centre of the earth. 

The fixed stars are so called because the an- 
cients believed they never changed their positions 
in respect to each other. Although their motions 
are very slow and almost imperceptible, yet the 
skilful and assiduous observations of modern as- 
tronomers, and particularly of Herschel, have prov- 
ed that many of them do change their mutual 
relations in a sensible degree. 

There is nothing so well calculated as the study 
of the stars to impress us with an idea of the im- 
mensity of space. Suppose when the earth is at a 
certain part of her orbit, we were to take the bear- 
ing of some star and note down accurately its 
angular direction from us, and when the earth had 
arrived at the opposite point in her orbit, that is, 
just six months after our observation, we were 
again to take the bearing of the same star and see 
how our real change of position had affected its 
apparent place. The nearer the star, the greater 
would be the angle these bearings make with each; 
the more distant the star, the less the angle. This 
angle, whatever be its magnitude, is called the 
annual parallax of the star. Now it has been 
found that this parallax is imperceptible with such 
instruments as the most skilful mechanic can con- 
struct. Suppose then a globe of fire, whose dia- 
meter should be equal to that of the earth's orbit, 
and whose circumference would consequently be 
six hundred millions of miles, situated where the 
earth now is, it would scarcely be seen from the 
nearest star, or only seen as a small luminous 
point. If the nearest of the stars are at such dis- 
tances, who will attempt to conceive the distance 
of those which we call the smaller and most dis- 
tant ! We shall take occasion to refer to this 
subject again hereafter. 

The brightness of the light of the stars situated 



16 



WONDERS OF THE HEAVENS, 



at such immense distances as they are proved to be, 
has induced astronomers to look upon them as cen- 
tres around which circulate systems imperceptible 
to us. Perhaps, also, (and this supposition will not 
appear destitute of probability to those who reflect 
on the infinite variety of phenomena which are dis- 
cerned in the dome above us,) these centres which 
carry with them through space their planetary sa- 
tellites, are themselves but satellites subject to the 
laws of other and more powerful primaries. We may 
be allowed to repeat that thought of Pascal, than 
which none can be more simple and sublime, and 
none express so well the extent of the universe ; 
It is a sphere whose centre is everywhere and whose 
circumference is nowhere. 



SECTION II. 

Divisiou of the stars according to their apparent magnitudes — Their 
number infinite — Impartial distribution over the heavens — Milky 
way — Distance of the stars — Their probable dimensions and nature 
— Periodical stars — Temporary stars — Double stars — Their revolu- 
tion round each other — Subject to the lavsrs of gravity — Colored 
stars — Proper motion of the stars — Compound sidereal systems — 
Clusters — Nebulae — Nebulous stars — Stars are visible in the day. 

The stars are arranged in several classes, ac- 
cording to their brightness ; the most brilliant 
being of the first magnitude, the next of the second, 
and so on up to the sixteenth magnitude. Only 
those of the first six classes are visible to the naked 
eye. The rest are called telescopic stars, from the 
instrument whose use is requisite to enable us to 
perceive them. 

In a clear night, we might suppose that the 
number of stars visible to the unassisted vision 
was immense ; but this is a deception, owing to 
the confusion produced by viewing at once or in 
rapid succession the different parts of the heaven. 
The images on the retina do not fade quick enough 
for our eyes to decide what number of bright points 
are really before them ; as the burning rod whirled 
rapidly round by the hand of a child presents to 
his delighted eyes the semblance of a continuous 
and fiery circle. The number actually discovera- 



ble without glasses, in either hemisphere, does not 
exceed thirteen hundred. But if we have recourse 
to a telescope, we shall discover an innumerable 
multitude of small stars, which before escaped our 
observation. Lalande observed 50,000, and Her- 
schel calculated that he saw 44,000 in a space of 
the heavens 8° long and 3° broad. Taking this as a 
basis, there would not be less than seventy-five 
millions in the whole heaven. There are, however, 
many more than this. It has been computed by 
some, that the telescope has made visible one hun- 
dred millions at least. All this vast assemblage of 
suns and worlds may bear no proportion to what 
lies beyond our ken. Count the leaves of the 
forest, the sands on the sea-shore, the drops in 
the ocean ; then may you think to set limits to 
the extent of God's creation ; then may you look 
on this earth as the universe, and not as a mere 
pebble on the shore of infinite space. 

It can be but one of the many mansions created 
for the accommodation of God's children. He may 
now, in regions beyond the imagination of the most 
gifted, be creating worlds more numerous than 
man can count, and more glorious than thought 
can fancy. 

There is no shadow of a reason for assigning any 
bounds to the number of the stars. Every increase 
in the dimension and power of instruments, which 
successive improvements in optical science have 
attained, having brought into view innumerable 
multitudes of objects invisible before. So that the 
number of the stars may be really infinite, in any 
sense we can apply to that word. 

The classification into magnitudes, however, it 
must be observed, is entirely arbitrary. Of a 
multitude of bright objects, differing probably 
intrinsically both in size and in splendor, and 
arranged at unequal distances from us, one must 
of necessity appear the brightest, one next below 
it, and so on. An order of succession (relative, of 
course, to our local situation among them) must 
exist, and it is a matter of absolute indifference 
where, in that infinite progression downwards, 
from the one brightest to the invisible, we choose 
to draw our lines of demarkation. All this is a 



WONDERS OF THE HEAVENS. 



17 



matter of pure convention. Usage, however, has 
established such a convention, and though it is 
impossible to determine exactly where one magni- 
tude ends and the next begins, and although diffe- 
rent observers have differed in their magnitudes, 
yet, on the whole, astronomers have restricted their 
first magnitude to about 15 or 20 principal stars; 
their second to 50 or 60 next inferior; their third 
to about 200 yet smaller, and so on; the numbers 
increasing very rapidly as we descend in the scale 
of brightness, the whole number of stars already 
registered, down to the seventh magnitude inclu- 
sive, amounting to 15,000 or 20,000. 

As we do not see the actual disc of a star, but 
judge only of its brightness by the total impression 
made upon the eye, the apparent magnitude of 
any star will, it is evident, depend, 1. on the star's 
distance from us ; 2. on the absolute magnitude of 
its illuminated surface ; 3. on the intrinsic bright- 
ness of that surface. Now, as we know nothing, 
or next to nothing, of any of these data, and have 
every reason for believing that each of them may 
differ in different individuals, in the proportion of 
many millions to one, it is clear that we are not 
to expect much satisfaction in any conclusions 
we may draw from numerical statements of the 
number of individuals arranged in our artificial 
classes. 

If the comparison of the apparent magnitudes of 
the stars with their numbers leads to no definite 
conclusion, it is otherwise when we view them in 
connection with their local distribution over the 
heavens. If indeed we confine ourselves to the 
three or four brightest classes, we shall find them 
distributed with tolerable impartiality over the 
sphere ; but if we take in the whole amount visible 
to the naked eye, we shall perceive a great and 
rapid increase of number as we approach the bor- 
ders of the milky way. And when we come to 
telescopic magnitudes, we find them crowded be- 
yond imagination along the extent of that circle, 
and of the branch which it sends off from it ; so 
that in fact its whole light is composed of nothing 
but stars, whose average magnitude may be stated 

at about the tenth or eleventh. 
3 



These phenomena agree with the supposition 
that the stars of our firmament, instead of being 
scattered in all directions indifferently through 
space, form a stratum, of which the thickness is 
small, in comparison with its length and breadth ; 
and in which the earth occupies a place somewhere 
about the middle of its thickness, and near the 
point where it subdivides into two principal laminae, 
inclined at a small angle to each other. For it is 
certain that, to an eye so situated, the apparent 
density of the stars, supposing them pretty equally 
scattered through the space they occupy, would 
be least in a direction of the visual ray (as S A) 
perpendicular to the lamina, and greatest in that 

^ — ^^ 




of its breadth, as S B, S C, S D ; increasing rapidly 
in passing from one to the other direction, just as 
we see a slight haze in the atmosphere thickening 
into a decided fog bank near the horizon, by the 
rapid increase of the mere length of the visual ray. 
Accordingly, such is the view of the construction 
of the starry firmament taken by Sir William Her- 
schel, whose powerful telescopes have effected a 
complete analysis of this wonderful zone, and 
demonstrated the fact of its entirely consisting of 
stars. So crowded are they in some parts of it, 
that by counting the stars in a single field of his 
telescope, he was led to conclude that 50,000 had 
passed under his review in a zone two degrees in 
breadth, during a single hour's observation. The 
immense distances at which the remoter regions 
must be situated will sufficiently account for the 
vast predominance of small magnitudes which are 
observed in it. 

When we speak of the comparative remoteness 
of certain regions of the starry heavens beyond 
others, and of our own situation in them, the ques- 
tion immediately arises. What is the distance of 
the nearest fixed star ? What is the scale on 
which our visible firmament is constructed ? And 
what proportion do its dimensions bear to those of 



gyg^-gaWMM'ML' O 



18 



WONDERS OF THE HEAVENS 



our own immediate system ? To this, however, 
astronomy has hitherto proved unable to supply an 
answer. All we know on the subject is negative. 
We have attained, by delicate observations and 
refined combinations of theoretical reasoning, to a 
correct estimate, first, of the dimensions of the 
earth ; then, taking that as a base, to a knowledge 
of those of its orbit about the sun ; and again, by 
taking our stand, as it were, on the opposite bor- 
ders of the circumference of this orbit, we have 
extended our measurements to the extreme verge 
of our own system, and by the aid of what we know 
of the excursions of comets, have felt our way, as 
it were, a step or two beyond the orbit of the 
remotest known planet. But between that re- 
motest orb and the nearest star there is a gulf 
fixed, to whose extent no observations yet made 
have enabled us to assign any distinct approxima- 
tion, or to name any distance, however immense, 
which it may not, for any thing we can tell, 
surpass. 

The diameter of the earth has served us as the 
base of a triangle, in the trigonometrical survey of 
our system, by which to calculate the distance of 
the sun ; but the extreme minuteness of the sun's 
parallax renders the calculation from this " ill-con- 
ditioned" triangle so delicate, that nothing but the 
fortunate combination of favorable circumstances, 
afforded by the transits of Venus, could render its 
results even tolerably worthy of reliance. But 
the earth's diameter is too small a base for direct 
triangulation to the verge even of our own system ; 
and we are, therefore, obliged to substitute the 
annual parallax for the diurnal, or, which comes to 
the same thing, to ground our calculation on the 
relative velocities of the earth and planets in their 
orbits, when we would push our triangulation to 
that extent. It might be naturally enough expect- 
ed, that by this enlargement of our base to the vast 
diameter of the earth's orbit, the next step in our 
survey would be made at a great advantage ; that 
our change of station, from side to side of it, would 
produce a perceptible and measurable amount of 
annual parallax in the stars, and that by its means 
we should come to a knowledge of their distance. 



But, after exhausting every refinement of observa- 
tion, astronomers have been unable to come to any 
positive and coincident conclusion upon this head ; 
and it seems, therefore, demonstrated, that the 
amount of such parallax, even for the nearest fixed 
star which has hitherto been examined with the 
requisite attention, remains still mixed up with, 
and concealed among, the errors incidental to all 
astronomical determinations. Now, such is the 
nicety to which these have been carried, that did 
the quantity in question amount to a single second, 
( i. e. did the radius of the earth's orbit subtend at 
the nearest fixed star that minute angle,) it could 
not possibly have escaped detection and universal 
recognition.* 

Radius is to the sine of V\ in round numbers, as 
200,000 to 1. In this proportion, then, at least, 
must the distance of the fixed stars fi'om the sun 
exceed that of the sun fi:'ora the earth. The latter 
distance, as we shall hereafter see, exceeds the 
earth's radius in the proportion of 24,000 to 1 ; 
and, lastly, to descend to ordinary standards, the 
earth's radius is 4,000 of our miles. The distance of 
the stars, then, cannot be so small as 4,800,000,000 
radii of the earth, or 19,200,000,000,000 miles ! 
How much larger it may be we know not. 

In such numbers the imagination is lost. The 
only mode we have of conceiving such intervals at 
all is by the time which it would require for light to 
traverse them. Now light, as we know, travels at 
the rate of 192,000 miles per second. It would, 
therefore, occupy 100,000,000 seconds, or upwards 
of three years, in such a journey, at the very low- 

* Astronomers are generally agreed in the opinion that the annual 
parallax of the stars is less than 1", and consequently that the near- 
est of them is placed at a much greater distance from us than these 
calculations make it. It was, however, announced within a few 
years, that M. D'Assas, a French astronomer, had satisfactorily esta- 
blished the annual parallax of Kcid (a small star eight degrees north 
of Gamma Eridani) to be 2", that of Rigel in Orion 1". 43, and that 
of Sirius 1". 24. If these results may he relied on, then Keid is but 
10,000,000,000,000 miles from the earth, Rigel but 13,708,524,066,400, 
and Sirius 15,809,023,721,735 miles. A distance, however, so great 
that if it were to fall towards the earth at the rate of a million of 
miles a day, it would take it forty-three thousand three hundred 
years to reach the earth ; or if the Almighty were now to blot it out 
of the heavens, its brilliancy would continue undiminished in our 
hemisphere for the space of three years ! 



WONDERS OF THE HEAVENS. 



19 



est estimate. What, then, are we to allow for the 
distance of those innumerable stars of the smaller 
magnitude which the telescope discloses to us ! If 
we admit the light of a star of each magnitude to 
be half that of the magnitude next above it, it will 
follow that a star of the first magnitude will require 
to be removed to 362 times its distance to appear 
no larger than one of the sixteenth. It follows, 
therefore, that among the countless multitude of 
such stars visible in telescopes, there must be 
many whose light has taken at least a thousand years 
to reach us ; and that when we observe their places, 
and note their changes, we are, in fact, reading 
only their history of a thousand years' date, thus 
wonderfully recorded. We cannot escape this con- 
clusion, but by adopting as an alternative an in- 
trinsic inferiority of light in all the smaller stars of 
the milky way. We shall be better able to esti- 
mate the probability of this alternative, when we 
have made acquaintance with other sidereal systems, 
whose existence the telescope discloses to us, and 
whose analogy will satisfy us that the view of the 
subject we have taken above is in perfect harmony 
with the general tenor of astronomical facts. 

Quitting, however, the region of speculation, 
and confining ourselves within certain limits which 
we are sure are less than the truth, let us employ 
the negative knowledge we have obtained respect- 
ing the distances of the stars to form some conforma- 
ble estimate of their real magnitudes. Of this, 
telescopes afford us no direct information. The 
discs which good telescopes show us- of the stars 
are not real, but spurious, a mere optical illusion. 
Their light, therefore, must be our only guide. 
Now Dr. Wollaston, by direct photometrical experi- 
ments, open, as it would seem, to no objections, has 
ascertained the light of Sirius, as received by us, to 
be to that of the sun as 1 to 20,000,000,000. The 
sun, therefore, in order that it should appear to us 
no brighter than Sirius, would require to be re- 
moved to 141,400 times its actual distance. We 
have seen, however, that the distance of Sirius can- 
not be so small as 200,000 times that of the sun. 
Hence it follows, that, upon the lowest possible 
computation, the light really thrown out by Sirius 



cannot be so little as double that emitted by the 
sun ; or that Sirius must, in point of intrinsic 
splendor, be at least equal to two suns, and is in 
all probability vastly greater.* 

Now, for what purpose are we to suppose such 
magnificent bodies scattered through the abyss of 
space ? Surely not to illuminate our nights, which 
an additional moon of the thousandth part of the 
size of our own would do much better, nor to 
sparkle as a pageant void of meaning and reality, 
and bewilder us among vain conjectures. Useful, 
it is true, they are to man as points of exact and 
permanent reference ; but he must have studied 
astronomy to little purpose, who can suppose man 
to be the only object of his Creator's care, or who 
does not see in the vast and wonderful apparatus 
around us provision for other races of animated 
beings. The planets, as we have seen, derive their 
light from the sun ; but that cannot be the case 
with the stars. These, doubtless, then, are them- 
selves suns, and may, perhaps, each in its sphere, 
be the presiding centre round which other planets, 
or bodies of which we can form no conception from 
any analogy offered by our own system, may be 
circulating. 

Analogies, however, more than conjectural, are 
not wanting to indicate a correspondence between 
the dynamical laws which prevail in the remote 
regions of the stars and those which govern the 
motions of our own system. Wherever we can 
trace the law of periodicity — the regular re- 
currence of the same phenomena in the same times 
— we are strongly impressed with the idea of 
rotary or orbitual motion. Among the stars are 
several which, though no way distinguishable fi'om 
others by any apparent change of place, nor by any 
difference of appearance in telescopes, yet undergo 
a regular periodical increase and diminution of 
lustre, involving, in one or two cases, a complete 
extinction and revival. These are called periodical 
stars. One of the most remarkable is the star Omi- 



* Dr. Wollaston, assuming, as he is perfectly justified in doing, a 
much lower limit of possible parallax in Sirius than we have adopted 
in the text, has concluded the intrinsic light of Sirius to he nearly 
that of fourteen suns. 



20 



WONDERS OF THE HEAVENS 



L 



cron, in the constellation Cetus, first noticed by 
Fabricius in 1596. It appears about twelve times 
in eleven years, or, more exactly, in a period of 
334 days ; remains at its greatest brightness about 
a fortnight, being then, on some occasions, equal 
to a large star of the second magnitude ; decreases 
during about three months, till it becomes complete- 
ly invisible, in which state it remains during about 
five months, when it again becomes visible, and 
continues increasing during the remaining three 
months of its period. Such is the general course 
of its phases. It does not always, however, return 
to the same degree of brightness, nor increase and 
diminish by the same gradations. Hevelius, indeed, 
relates that during the four years between October, 
1672, and December, 1676, it did not appear at all. 
Another very remarkable periodical star is that 
called Algol. It is usually visible as a star of the se- 
cond magnitude, and such it continues for the space 
of two days and fourteen hours, when it suddenly be- 
gins to diminish in splendor, and in about three and 
a half hours is reduced to the fourth magnitude. It 
then begins again to increase, and in three and a half 
hours more is restored to its usual brightness, going 
through all its changes in two days, twenty hours, 
forty-eight minutes, or thereabouts. This remarka- 
ble law of variation certainly appears strongly to 
suggest the revolution round it of some opaque body, 
which, when interposed between us and Algol, cuts 
off a large portion of its light ; and this is accord- 
ingly the view taken of the matter by Goodricke, 
to whom we owe the discovery of this remarkable 
fact, in the year 1782 ; since which time the same 
phenomena have continued to be observed, though 
with much less diligence than their high interest 
would appear to merit. Taken any how, it is an 
indication of a high degree of activity^ in regions 
where, but for such evidences, we might conclude 
all lifeless. Our own sun requires nine times this 
period to perform a revolution on its own axis. On 
the other hand, the periodic time of an opaque re- 
volving body, sufficiently large, which should pro- 
duce a similar temporary obscuration of the sun, 
seen from a fixed star, would be less than fourteen 
hours. 



There are many other variable stars, with great 
differences in the periods of their changes. It is 
not requisite to enumerate them in this work. 

The variations of these stars, however, appear 
to be affected, perhaps in duration of period, but 
certainly in extent of change, by physical causes at 
present unknown. The non-appearance of Omicron 
Ceti, during four years, has already been noticed; 
and to this instance we may add that of Chi Cygni, 
which is stated by Cassini to have been scarcely 
visible throughout the years 1699, 1700, and 1701, 
at those times when it ought to have been most 
conspicuous. 

These irregularities prepare us for other phe- 
nomena of stellar variation, which have hitherto 
been reduced to no law of periodicity, and must be 
looked upon, in relation to our ignorance and inex- 
perience, as altogether casual ; or, if periodic, of 
periods too long to have occurred more than once 
within the limits of recorded observation. The 
phenomena we allude to are those of temporary 
stars, which have appeared, from time to time, in 
different parts of the heavens, blazing forth with 
extraordinary lustre ; and after remaining aAvhile 
apparently immovable, have died away, and left 
no trace. Such is the star which, suddenly appear- 
ing in the year 125 B. C, is said to have attracted 
the attention of Hipparchus, and led him to draw 
up a catalogue of stars, the earliest on record. 
Such, too, was the star which blazed forth, A. D. 
389, near Alpha Aquilae, remaining for three weeks 
as bright as Venus, and disappearing entirely. In 
the years 945, 1264, and 1572, brilliant stars ap- 
peared in the region of the heavens between Ce- 
pheus and Cassiopeia ; and, from the imperfect 
account we have of the places of the two earlier, as 
compared with that of the last, which was well 
determined, as well as from the tolerably near 
coincidence of the intervals of their appearance, 
we may suspect them to be one and the same star, 
with a period of about 300, or, as Goodricke sup- 
poses, of 150 years. The appearance of the star 
of 1572 was so sudden, that Tycho Brahe, a cele- 
brated Danish astronomer, returning one evening 
(the 11th of November) from his laboratory to his 



WONDERS OF THE HEAVENS 



21 



dwelling-house, was surprised to find a group of 
country people gazing at a star, which he was sure 
did not exist half an hour before. This was the 
star in question. It was then as bright as Sirius, 
and continued to increase till it surpassed Jupiter 
when brightest, and was visible at mid-day. It 
began to diminish in December of the same year, 
and in March, 1574, had entirely disappeared. So, 
also, on the 10th of October, 1604 a star of this 
kind, and not less brilliant, burst forth in the con- 
stellation of Serpentarius, which continued visible 
till October, 1605. 

Similar phenomena, though of a less splendid 
character, have taken place more recently, as in 
the case of the star of the third magnitude discover- 
ed in 1670, by Anthelm, in the head of the Swan; 
which, after becoming completely invisible, reap- 
peared, and after undergoing one or two singular 
fluctuations of light, during two years, at last died 
away entirely, and has not since been seen. On a 
careful re-examination of the heavens, too, and a 
comparison of catalogues, many stars are now found 
to be missing ; and although there is no doubt that 
these losses have often arisen from mistaken entries, 
yet in many instances it is equally certain that 
there is no mistake in the observation or entry, 
and that the star has really been observed, and as 
really has disappeared fi-om the heavens. This is 
a branch of practical astronomy which has been too 
little followed up, and it is precisely that in which 
amateurs of the science, provided with only good 
eyes, or moderate instruments, might employ their 
time to excellent advantage. It holds out a sure 
promise of rich discovery, and is one in which 
astronomers in establishing observatories are almost 
fif necessity precluded fi-om taking a part by the 
nature of the observations required. Catalogues 
of the comparative brightness of the stars in each 
constellation have been constructed by Sir William 
Herschel, with the express object of facilitating 
these researches. 

We come now to a class of phenomena of quite 
a different character, and which give us a real and 
positive insight into the nature of at least some 
among the stars, and enable us unhesitatingly to 



declare them subject to the same dynamical laws, 
and obedient to the same power of gravitation, 
which governs our own system. Many of the stars, 
when examined with telescopes, are found to be 
double, i. e. to consist of two (in some cases three) 
individuals placed near together. This might be 
attributed to accidental proximity, did it occur only 
in a few instances; but the frequency of this com- 
panionship, the extreme closeness, and, in many 
cases, the near equality of the stars so conjoined, 
would alone lead to a strong suspicion of a more 
near and intimate relation than mere casual juxta- 
position. The bright star Castor, for example, 
when much magnified, is found to consist of two 
stars of between the third and fourth magnitude, 
within 5" of each other. Stars of this magnitude, 
however, are not so common in the heavens as to 
render it at all likely that, if scattered at random, 
any two would fall so near. But this is only one 
out of numerous such instances. Sir William Her- 
schel has enumerated upwards of 500 double stars, 
in which the individuals are within half a minute of 
each other; and to this list Professor Struve, prose- 
cuting the inquiry by the aid of instruments more 
conveniently mounted for the purpose, has recently 
added nearly five times that number. Other ob- 
servers have still further extended the catalogue, 
already so large, without exhausting the fertility 
of the heavens. Among these are great numbers 
in which the interval between the centres of the 
individuals is less than a single second. They are 
divided into classes according to their distances, 
the closest forming the first class. 

When these combinations were first noticed, it 
was considered that advantage might be taken of 
them, to ascertain whether or not the annual mo- 
tion of the earth in its orbit might not produce a 
relative apparent displacement of the individuals 
constituting a double star. Supposing them to lie 
at a great distance one behind the other, and to 
appear only by casual juxtaposition nearly in the 
same line, it is evident that any motion of the earth 
must subtend different angles at the two stars so 
juxtaposed, and must therefore produce different 
parallactic displacements of them on the surface of 



22 



WONDERS OF THE HEAVENS 



the heavens, regarded as mfinitely distant. Every 
star, in consequence of the earth's annual motion, 
should appear to describe in the heavens a small 
ellipse, (distinct from that which it would appear to 
describe in consequence of the aberration of light, 
and not to be confounded with it,) being a section, 
by the concave surface of the heavens, of an oblique 
elliptic cone, having its vertex in the star, and the 
earth's orbit for its base ; and this section will be 
of less dimensions the more distant is the star. If, 
A 



/ 


\ 


Q 


/ \ 


1^ 


'Yn 






4 S ] 




B 


y 



then, we regard two stars, apparently situated close 
beside each other, but in reality at very different 
distances, their parallactic ellipses will be similar, 
but of different dimensions. Suppose, for instance, 
S and s to be the positions of two stars of such an 
apparently or optically double star as seen from the 
sun, and let A B C D, abed, be their parallactic 
ellipses ; then, since they will be at all times simi- 
larly situated in these ellipses, when the one star 
is seen at A, the other will be seen at a. When 
the earth has made a quarter of a revolution in its 
orbit, their apparent places will be Bb; when 
another quarter, Cc; and when another, D t?. If, 
then, we measure carefully, with micrometers 
adapted for the purpose, their apparent situation 
with respect to each other, at different times of the 
year, we should perceive a periodical change, both 
in the direction of the line joining them, and in the 
distance between their centres. For the lines A a 
and C c cannot be parallel, nor the lines B b and D d 
equal, unless the ellipses be of equal dimensions, 
i. e. unless the two stars have the same parallax, or 
are equidistant from the earth. 



Now, micrometers, properly mounted, enable us 
to measure very exactly both the distance between 
two objects which can be seen together in the same 
field of a telescope, and the position of the line 
joining them with respect to the horizon, or the 
meridian, or any other determinate direction in the 
heavens. The meridian is chosen as the most con- 
venient ; and the situation of the line of junction 
between the two stars of a double star is referred 
to its direction, by placing in the focus of the eye- 
piece of a telescope, equatorially mounted, two 
cross wires making a right angle, and adjusting 
their position so that one of the two stars shall just 
run along it by its diurnal motion, while the tele- 
scope remains at rest ; noting their situation ; and 
then turning the whole system of wires round in its 
own plane by a proper mechanical movement, till 
the other wire becomes exactly parallel to their 
line of junction, and reading off on a divided circle 
the angle the wires have moved through. Such an 
apparatus is called a position micrometer ; and by 
its aid we determine the angle of position of a double 
star, or the angle which their line of junction makes 
with the meridian ; which angle is usually reckon- 
ed round the whole circle, from to 360. 

The advantages which this mode of operation 
offers for the estimation of parallax are many and 
great. In the first place, the result to be obtained, 
being dependent only on the relative apparent dis- 
placement of the two stars, is unaffected by almost 
every cause which would induce error in the sepa- 
rate determination of the place of either by right 
ascension and declination. Refraction, that great- 
est of all obstacles to accuracy in astronomical 
determinations, acts equally on both stars ; and is 
therefore eliminated from the result. We have no 
longer any thing to fear from errors of graduation in 
circles, from levels or plumb-lines, from uncertainty 
attending the uranographical reductions of aberra- 
tion, precession, &,c., all which bear alike on both 
objects. In a word, if we suppose the stars to have 
no proper motions of their own by which a real 
change of relative situation may arise, no other 
cause but their difference of parallax can possibly 
affect the observation. 



WONDERS OF THE HEAVENS 



23 



Such were the considerations which first induced 
Sir William Herschel to collect a list of double 
stars, and to subject them all to careful measure- 
ments of their angles of position and mutual dis- 
tances. He had hardly entered, however, on these 
measurements, before he was diverted from the 
original object of the inquiry (which, in fact, 
promising as it is, still remains open and untouched, 
though the only method which seems to offer a 
chance of success in the research of parallax) by 
phenomena of a very unexpected character, which 
at once engrossed his whole attention. Instead of 
finding, as he expected, that annual fluctuation to 
and fro of one star of a double star with respect 
to the other, that alternate annual increase and 
decrease of their distance and angle of position, 
which the parallax of the earth's annual motion 
would produce, he observed, in many instances, a 
regular progressive change ; in some cases bearing 
chiefly on their distance, in others on their posi- 
tion, and advancing steadily in one direction, so as 
clearly to indicate either a real motion of the stars 
themselves, or a general rectilinear motion of the 
sun and whole solar system, producing a parallax 
of a higher order than would arise from the earth's 
orbitual motion, and Avhich might be called syste- 
matic parallax. 

Supposing the two stars in motion independently 
of each other, and also the sun, it is clear that for 
the interval of a few years, these motions must be 
regarded as rectilinear and uniform. Hence a 
very slight acquaintance with geometry will suffice 
to show that the apparent motion of one star of a 
double star, referred to the other as a centre, and 
mapped down, as it were, on a plane in which that 
other shall be taken for a fixed or zero point, can 
be no other than a right line. This, at least, must 
be the case if the stars be independent of each 
other ; but it will be otherwise if they have a phy- 
sical connection, such as, for instance, real proximi- 
ty and mutual gravitation would establish. In that 
case, they would describe orbits round each other, 
and round their common centre of gravity ; and 
therefore the apparent path of either, referred to 
the other as fixed, instead of being a portion of a 



straight line, would be bent into a curve concave 
towards that other. The observed motions, how- 
ever, were so slow, that many years' observation 
was required to ascertain this point ; and it was 
not, therefore, until the year 1803, twenty-five 
years from the commencement of the inquiry, that 
any thing like a positive conclusion could be come 
to, respecting the rectilinear or orbitual character 
of the observed changes of position. 

In that, and the subsequent year, it was dis- 
tinctly announced by Sir William Herschel, in two 
papers, that there exist sidereal systems, composed 
of two stars revolving about each other in regular 
orbits, and constituting what may be termed binary 
stars, to distinguish them from double stars general- 
ly so called, in which these physically connected 
stars are confounded, perhaps, with others only 
optically double, or casually juxtaposed in the hea- 
vens at different distances from the eye ; whereas 
the individuals of a binary star are, of course, equi- 
distant from the eye, or, at least, cannot differ 
more in distance than the semidiameter of the orbit 
they describe about each other, which is quite in- 
significant compared with the immense distance 
between them and the earth. Between fifty and 
sixty instances of changes, to a greater or less 
amount, in the angles of position of double stars, 
are adduced in the memoirs above • mentioned ; 
many of which are too decided, and too regularly 
progressive, to allow of their nature being miscon- 
ceived. In particular, among the more conspicu- 
ous stars. Castor, Gamma Virginis, Xi Ursae, 70 
Ophiuchi, Sigma Coronse, Eta Cassiopeise, Gamma 
Leonis, Lambda Ophiuchi, and Zeta Aquarii, are 
enumerated as among the instances of the observed 
motion ; and to some of them even periodic times 
of revolution are assigned, approximative only, of 
course, and rather to be regarded as rough guesses 
than as results of any exact calculation, for which 
the data were at the time quite inadequate. For 
instance, the revolution of Castor is set down at 
334 years, that of Gamma Virginis at 708, and that 
of Gamma Leonis at 1200 years. 

Subsequent observation has fully confirmed these 
results, not only in their general tenor, but for the 



24 



WONDERS OF THE HEAVENS 



most part in individual detail. Of all the stars 
above named, there is not one which is not found to 
be fully entitled to be regarded as binary ; and, in 
fact, this list comprises nearly all the most conside- 
rable objects of that description w^hich have yet 
been detected, though (as attention has been closely 
drawn to the subject, and observations have multi- 
plied) it has, of late, begun to extend itself rapidly. 
The number of double stars which are certainly 
known to possess this peculiar character is between 
thirty and forty, and more are emerging into notice 
with every fresh mass of observations which comes 
before the public. They require excellent tele- 
scopes for their observation, being for the most 
part so close as to necessitate the use of very high 
magnifiers to perceive an interval between the in- 
dividuals which compose them. 

It may easily be supposed, that phenomena of 
this kind would not pass without attempts to con- 
nect them with dynamical theories. From their 
first discovery, they were naturally referred to the 
agency of some power, like that of gravitation, con- 
necting the stars thus demonstrated to be in a state 
of circulation about each other ; and the extension 
of the Newtonian law of gravitation to these remote 
systems was a step so obvious, and so well warrant- 
ed by our experience of its all-sufficient agency in 
our own, as to have been expressly or tacitly made 
by every one who has given the subject any share 
of his attention. We owe, however, the first dis- 
tinct system of calculation, by which the elliptic 
elements of the orbit of a binary star could be de- 
duced from observations of its angle of position and 
distance at different epochs, to M. Savary, who 
showed, that the motions of one of the most re- 
markable among them were explicable, within the 
limits allowable for error of observation, on the 
supposition of an elliptic orbit described in the short 
period of fifty-eight and one fourth years. A dif- 
ferent process of computation has conducted pro- 
fessor Encke to an elliptic orbit for 70 Ophiuchi, 
described in a period of seventy-four years ; and Sir 
John Herschel's skill has not failed to add others 
to the number. 

Of these, perhaps, the most remarkable is Gamma 



Virginis, not only on account of the length of its 
period, but by reason also of the great diminution 
of apparent distance, and rapid increase of angular 
motion about each other, of the individuals com- 
posing it. It is a bright star of the fourth magni- 
tude, and its component stars are almost exactly 
equal. It has been known to consist of two stars 
since the beginning of the eighteenth century, their 
distance being then between six and seven seconds ; 
so that any tolerably good telescope would resolve 
it. Since that time they have been constantly ap- 
proaching, and are at present hardly more than a 
single second asunder ; so that no telescope, that 
is not of very superior quality, is competent to 
show them otherwise than as a single star some- 
what lengthened in one direction. It fortunately 
happens, that Bradley, in 1718, noticed, and re- 
corded in the margin of one of his observation 
books, the apparent direction of their line of junc- 
tion, as being parallel to that of two remarkable stars. 
Alpha and Delta of the same constellation, as seen 
by the naked eye ; and this note, which has been 
recently rescued from oblivion by the diligence of 
professor Rigaud, has proved of signal service in 
the investigation of their orbit. They are entered 
also as distinct stars in Mayer's catalogue ; and 
this affords also another means of recovering their 
relative situation at the date of his observations, 
which were made about the year 1756. 

If the great length of the periods of some of these 
bodies be remarkable, the shortness of those of 
others is hardly less so. Eta Coronge has already 
made a complete revolution since its first discovery 
by Sir William Herschel, and is far advanced in its 
second period ; and Xi Ursae, Zeta Cancri, and 70 
Ophiuchi, have all accomplished by far the greater 
parts of their respective ellipses since the same 
epoch. If any doubt, therefore could remain as to 
the reality of their orbitual motions, or any idea of 
explaining them by mere parallactic changes, these 
facts must suffice for their complete dissipation. 
We have the same evidence, indeed, of their rota- 
tions about each other that we have of those of Ura- 
nus and Saturn about the sun ; and the correspon- 
dence between their calculated and observed places 



WONDERS OF THE HEAVENS 



25 



in such very elongated ellipses, must be admitted 
to carry with it a proof of the prevalence of the 
Nev^^tonian lavv^ of gravity in their systems, of the 
very same nature and cogency as that of the calcu- 
lated and observed places of comets round the cen- 
tral body of our own. 

But it is not with the revolutions of bodies of a 
planetary or cometary nature round a solar centre 
that we are now concerned ; it is with that of sun 
around sun, each, perhaps, accompanied with its 
train of planets and their satellites, closely shrouded 
from our view by the splendor of their respective 
suns, and crowded into a space bearing hardly a 
greater proportion to the enormous interval which 
separates them, than the distances of the satellites 
of our planets from their primaries bear to their 
distances from the sun itself A less distinctly 
characterized subordination would be imcompatible 
with the stability of their systems, and with the 
planetary nature of their orbits. Unless closely 
nestled under the protecting wing of their imme- 
diate superior, the sweep of their other sun in its 
perihelion passage round their own might carry 
them off, or whirl them into orbits utterly incom- 
patible with the conditions necessary for the exist- 
ence of their inhabitants. It must be confessed, 
that we have here a strangely wide and novel field 
for speculative excursions, and one which it is not 
easy to avoid luxuriating in. 

Many of the double stars exhibit the curious and 
beautiful phenomenon of contrasted or complemen- 
tary colors. In such instances, the larger star is 
usually of a ruddy or orange hue, while the smaller 
one appears blue or green, probably in virtue of 
that general law of optics, which provides that when 
the retina is under the influence of excitement by 
any bright, colored light, feebler lights, which 
seen alone would produce no sensation but of white- 
ness, shall for the time appear colored with the 
tint complementary to that of the brighter. Thus, 
a yellow color predominating in the light of the 
brighter star, that of the less bright one in the 
same field of view will appear blue ; while, if the 
tint of the brighter star verge to crimson, that of 

the other will exhibit a tendency to green, or even 
4 



appear as a vivid green, under favorable circum- 
stances. The former contrast is beautifully exhibit- 
ed by Iota Cancri, the latter by Gamma Andromedse; 
both fine double stars. If, however, the colored 
star be much the less bright of the two, it will not 
materially affect the other. Thus, for instance, 
Eta Cassiopeiae exhibits the beautiful combination 
of a large white star, and a small one of a rich 
ruddy purple. It is by no means, however, intend- 
ed to say, that in all such cases one of the colors 
is a mere effect of contrast ; and it may be easier 
suggested in words, than conceived in imagination, 
what variety of illumination two suns, a red and a 
green, or a yellow and a blue one, must afford a 
planet circulating about either ; and what charm- 
ing contrasts and "grateful vicissitudes" — a red 
and a green day, for instance, alternating with a 
white one and with darkness — might arise from the 
presence or absence of one or other, or both, above 
the horizon. Insulated stars of a red color, almost 
as deep as that of blood, occur in many parts of 
the heavens, but no green or blue star (of any 
decided hue) has, we believe, ever been noticed 
unassociated with a companion brighter than itself. 
Another very interesting subject of inquiry, in 
the physical history of the stars, is their proper 
motion. It might be expected that apparent mo- 
tions of some kind or other should be detected 
among so great a multitude of individuals scattered 
through space, and with nothing to keep them fixed. 
Their mutual attractions even, however inconceiva- 
bly enfeebled by distance, and counteracted by 
opposing attractions from opposite quarters, must, 
in the lapse of countless ages, produce some move- 
ments, some change of internal arrangement, re- 
sulting from the difference of the opposing actions. 
And it is a fact, that such apparent motions do 
exist, not only among single, but in many of the 
double stars ; which, besides revolving round each 
other, or round their common centre of gravity, 
are transferred, without parting company, by a 
progressive motion common to both, towards some 
determinate region. For example, the two stars 
of 61 Cygni, which are nearly equal, have remain- 
ed constantly at the same, or very nearly the same. 



26 



WONDERS OF THE HEAVENS. 



distance, of 15" for at least fifty years past. 
Meanwhile they have shifted their local situation in 
the heavens, in this interval of time, through no less 
than 4' 23", the annual proper motion of each star 
being 5". 3 ; by which quantity (exceeding a third 
of their interval) this system is every year carried 
bodily along in some unknown path, by a motion 
which, for many centuries, must be regarded as 
uniform and rectilinear. Among stars not double, 
and no way differing fi-om the rest in any other 
obvious particular, Mu Cassiopeise is to be remark- 
ed as having the greatest proper motion of any yet 
ascertained, amounting to 3". 74 of annual displace- 
ment. And a great many others have been ob- 
served to be thus constantly carried away from 
their places by smaller, but not less unequivocal 
motions. 

Motions which require whole centuries to accu- 
mulate before they produce changes of arrange- 
ment, such as the naked eye can detect, though 
quite sufficient to destroy that idea of mathematical 
fixity which precludes speculation, are yet too 
trifling, as far as practical applications go, to induce 
a change of language, and lead us to speak of the 
stars in common parlance as otherwise than fixed. 
Too little is yet known of their amount and direc- 
tions, to allow of any attempt at referring them to 
definite laws. It may, however, be stated general- 
ly, that their apparent directions are various, and 
seem to have no marked common tendency to one 
point more than to another of the heavens. It was, 
indeed, supposed by Sir William Herschel, that 
such a common tendency could be made out ; and 
that, allowing for individual deviations, a general 
recess could be perceived in the principal stars, 
from that point occupied by the star Zeta Herculis, 
towards a point diametrically opposite. This gene- 
ral tendency was referred by him to a motion of the 
sun and solar system in the opposite direction. No 
one, who reflects with due attention on the subject, 
will be inclined to deny the high probability, nay 
certainty, that the sun has a proper motion in some 
direction ; and the inevitable consequence of such 
a motion, unparticipated by the rest, must be a slow 
average apparent tendency of all the stars to the 



vanishing point of lines parallel to that direction, 
and to the region which he is leaving. This is the 
necessary effect of perspective ; and it is certain 
that it must be detected by such observations, if 
we knew accurately the apparent proper motions 
of all the stars, and if we were sure that they were 
independent, i. e. that the whole firmament, or at 
least all that part which we see in our own neigh- 
borhood, were not drifting along together, by a 
general set, as it were, in one direction, the result 
of unknown processes and slow internal changes 
going on in the sidereal stratum to which our sys- 
tem belongs, as we see motes sailing in a current 
of air, and keeping nearly the same relative situa- 
tion with respect to one another. But it seems to 
be the general opinion of astronomers, at present, 
that their science is not yet matured enough to 
afford data for any secure conclusions of this kind 
one way or other. Meanwhile, a very ingenious 
idea has been suggested, viz. that a solar motion, 
if it exist, and have a velocity at all comparable to 
that of light, must necessarily produce a solar aber- 
ration ; in consequence of which we do not see the 
stars disposed as they really are, but too much 
crowded in the region the sun is leaving, too open 
in that he is approaching. Now this, so long as 
the solar velocity continues the same, must be a 
constant effect, which observation cannot detect ; 
but should it vary, in the course of ages, by a 
quantity at all commensurate to the velocity of the 
earth in its orbit, the fact would be detected by a 
general apparent rush of all the stars to the one or 
other quarter of the heavens, according as the sun's 
motion were accelerated or retarded ; which ob- 
servation would not fail to indicate, even if it should 
amount to no more than a very few seconds. This 
consideration, refined and remote as it is, may 
serve to give some idea of the delicacy and in- 
tricacy of any inquiry into the matter of proper 
motion ; since the last mentioned effect would ne- 
cessarily be mixed up with the systematic parallax, 
and could only be separated from it by considering 
that the nearer stars would be affected more than 
the distant ones by the one cause, but both near 
and distant alike by the other. 



WONDEUS OF THE HEAVENS 



27 



When we cast our eyes over the concave of the 
heavens in a clear night, we do not fail to observe 
that there are here and there groups of stars which 
seem to be compressed together in a more con- 
densed manner than in the neighboring parts, form- 
ing bright patches and clusters, which attract atten- 
tion, as if they were there brought together by 
some general cause other than casual distribution. 
There is a group, called the Pleiades, in which six 
or seven stars may be noticed, if the eye be direct- 
ed full upon it ; and many more \^ the eye be turned 
carelessly aside, while the attention is kept directed* 
upon the group. Telescopes show fifty or sixty 
large stars thus crowded together in a very mode- 
rate space, comparatively insulated from the rest 
of the heavens. The constellation called Coma 
Berenices is another such group, more diffused, and 
consisting of much larger stars. 

In the constellation Cancer there is a somewhat 
similar, but less definite, luminous spot, called 
Prsesepe, or the bee-hive, which a very moderate 
telescope — an ordinary night-glass, for instance — 
resolves entirely into stars. In the sword-handle 
of Perseus, also, is another such spot, crowded 
with stars, which requires rather a better telescope 
to resolve into individuals separated from each 
other. These are called clusters of stars ; and, 
whatever be their nature, it is certain that other 
laws of aggregation subsist in these spots, than 
those which have determined the scatterino; of stars 
over the general surface of the sky. This conclu- 
sion is still more strongly pressed upon us, when 
we come to bring very powerful telescopes to bear 
on these and similar spots. There are a great 
number of objects which have been mistaken for 
comets, and, in fact, have very much the appear- 
ance of comets without tails : small round or oval 

* It is a very remarkable fact, that the centre of the visual area is 
by far less sensible to feeble impressions of light, than the exterior 
portions of the retina. Few persons are aware of the extent to which 
this comparative insensibility extends, previous to trial. To appre- 
ciate it, let the reader look alternately full at a star of the fifth magni- 
tude, and beside it ; or choose two equally bright, and about three or 
four degrees apart, and look full at one of them, the probability is, he 
will see only the other. The fact accounts for the multitude of stars 
with which we are impressed by a general view of the heavens ; their 
paucity when we come to count them. 



nebulous specks, which telescopes of moderate 
power only show as such. Messier has given, in 
the Connois. des Temps for 1784, a list of the places 
of 103 objects of this sort ; which all those who 
search for comets ought to be familiar with, to 
avoid being misled by their similarity of appearance. 
That they are not, however, comets, their fixity 
sufliciently proves ; and when we come to examine 
them with instruments of great power, such as re- 
flectors of eighteen inches, two feet or more in 
aperture, any such idea is completely destroyed. 
They are then, for the most part, perceived to con- 
sist entirely of stars crowded together so as to oc- 
cupy almost a definite outline, and to run up to a 
blaze of light in the centre, where their condensa- 
tion is usually the greatest. The figure represents 




the thirteenth nebula of Messier's list, as seen in the 
twenty feet reflector at Slough.* Many of them, 
indeed, are of an exactly round figure, and convey 
the complete idea of a globular space filled full of 
stars, insulated in the heavens, and constituting in 
itself a family or society apart from the rest, and 
subject only to its own internal laws. It would be 
a vain task to attempt to count the stars in one of 
these globular dusters. They are not to be reckon- 
ed by hundreds : and on- a rough calculation, 
grounded on the apparent intervals between them 
at the borders, (where they are seen not projected 
on each other,) and the angular diameter of the 

* This beautiful object was first noticed by Halley in 1714. It is 
visible to the naked eye, between the stars Mu and Zeta Herculis. 
In a night-glass it appears exactly like a small round comet. 



28 



WONDERS OF THE HEAVENS. 



whole group, it would appear that many clusters 
of this description must contain, at least, ten or 
twenty thousand stars, compacted and wedged 
together in a round space, whose angular diameter 
does not exceed eight or ten minutes ; that is to 
say, in an area not more than a tenth part of that 
covered by the moon. 

Perhaps it may be thought to savor of the 
gigantesque to look upon the individuals of such a 
group as suns like our own, and their mutual dis- 
tances as equal to those which separate our sun 
from the nearest fixed star ; yet, when we consider 
that their united lustre affects the eye with a less 
impression of light than a star of the fifth or sixth 
magnitude, (for the largest of these clusters is bare- 
ly visible to the naked eye,) the idea we are thus 
compelled to form of their distance from us may 
render even such an estimate of their dimensions 
familiar to our imagination ; at all events, we can 
hardly look upon a group thus insulated, thus per- 
fect in itself, as not forming a system of a peculiar 
and definite character. Their round figure clearly 
indicates the existence of some general bond of 
union in the nature of an attractive force ; and in 
many of them there is an evident acceleration in 
the rate of condensation as we approach the centre, 
which is not referable to a merely uniform distribu- 
tion of equidistant stars through a globular space, 
but marks an intrinsic density in their state of aggre- 
gation greater at the centre than at the surface of 
the mass. It is difficult to form any conception of 
the dynamical state of such a system. On the 
one hand, without a rotary motion and a centri- 
fugal force, it is hardly possible not to regard them 
as in a state of progressive collapse. On the other, 
granting such a motion and such a force, we find it 
no less difficult to reconcile the apparent sphericity 
of their form with a rotation of the whole system 
round any single axis, without which internal colli- 
sions would appear to be inevitable. 

It is to Sir William Herschel that we owe the 
most complete analysis of the great variety of those 
objects which are generally classed under the com- 
mon head of nebulae, but which have been separat- 
ed by him into — 1st, Clusters of stars, in which 



the stars are clearly distinguishable ; and these, 
again, into globular and irregular clusters ; 2d, 
Resolvable nebulae, or such as excite a suspicion 
that they consist of stars, and which any increase 
of the optical power of the telescope may be ex- 
pected to resolve into distinct stars ; 3d, Nebulae 
properly so called, in which there is no appearance 
whatever of stars ; which, again, have been subdi- 
vided into subordinate classes, according to their 
brightness and size ; 4th, Planetary nebulae ; 5th, 
Stellar nebulae ; and, 6th, Nebulous stars. The 
great power of his telescopes has disclosed to us 
the existence of an immense number of these ob- 
jects, and shown them to be distributed over the 
heavens, not by any means uniformly, but, generally 
speaking, with a marked preference to a broad 
zone crossing the milky-way nearly at right angles. 
In some parts of this zone, indeed, — especially 
where it crosses the constellations Virgo, Coma 
Berenices, and the Great Bear, — they are assembled 
in great numbers ; being, however, for the most 
part telescopic, and beyond the reach of any but the 
most powerful instruments. 

Clusters of stars are either globular, such as we 
have already described, or of irregular figure. 
These latter are, generally speaking, less rich in 
stars, and especially less condensed towards the 
centre. They are also less definite in point of out- 
line ; so that it is often not easy to say where they 
terminate, or whether they are to be regarded 
otherwise than as merely richer parts of the hea- 
vens than those around them. In some of them 
the stars are nearly all of a size, in others extreme- 
ly different ; and it is no uncommon thing to find a 
very red star, much brighter than the rest, occupy- 
ing a conspicuous situation in them. Sir William 
Herschel regards these as globular clusters in a less 
advanced state of condensation, conceiving all such 
groups as approaching, by their mutual attraction, 
to the globular figure, and assembling together 
from all the surrounding region, under laws of 
which we have no other proof than the observance 
of a gradation by which their characters shade 
into one another, so that it is impossible to say 
where one species ends and the other begins. 



WONDERS OF THE HEAVENS 



29 



Resolvable nebulse can, of course, only be con- 
sidered as clusters either too remote, or consisting 
of stars intrinsically too faint to affect us by their 
individual light, unless where two or three happen 
to be close enough to make a joint impression, and 
give the idea of a point brighter than the rest. 
They are almost universally round or oval, their 
loose appendages, and irregularities of form, being 
as it were extinguished by the distance, and only 
the general figure of the more condensed parts 
being discernible. It is under the appearance of 
objects of this character that all the greater globu- 
lar clusters exhibit themselves in telescopes of in- 
sufiicient optical power to show them well ; and 
the conclusion is obvious, that those which the 
most powerful can barely render resolvable, Avould 
be completely resolved by a further increase of in- 
strumental force. 

Of nebulse, properly so called, the variety is 
again very great. By far the most remarkable are 



+ K 



4S^fe, 



Hi'' 



those represented in figures adjoining, the upper 
of which represents the nebulae surrounding the 



quadruple (or rather sextuple) star Theta in the 
constellation Orion ; the lower, that about Eta, in 
the southern constellation Robur Caroli : the one 
discovered by Huygens, in 1656, and figured as 
seen in the twenty feet reflector at Slough ; the 
other by Lacaille, from a figure by Mr. Dunlop. 
The nebulous character of these objects, at least 
of the former, is very different from what might be 
supposed to arise from the congregation of an im- 
mense collection of small stars. It is formed of 
little flocky masses, like wisps of cloud ; and such 
wisps seem to adhere to many small stars at its 
outskirts, and especially to one considerable star, 
(represented, in the figure, below the nebula,) 
which it envelopes with a nebulous atmosphere of 
considerable extent and singular figure. Several 
astronomers, on comparing this nebula with the 
figures of it handed down to us by its discoverer, 
Huygens, have concluded that its form has under- 
gone a perceptible change. But when it is consi- 
dered how difficult it is to represent such an object 
duly, and how entirely its appearance will differ, 
even in the same telescope, according to the clear- 
ness of the air, or other temporary causes, we shall 
readily admit that we have no evidence of change 
that can be relied on. 

The next figure represents a nebula of a quite 
different character. The original of this figure is 




in the constellation Andromeda, near the star Nu. 
It is visible to the naked eye, and is continually 
mistaken for a comet, by those unacquainted with 
the heavens. Simon Marius, who noticed it in 
1612, describes its appearance as that of a candle 



30 



WONDERS OF THE HEAVENS 



shining through horn, and the resemblance is not 
inapt. Its form is a pretty long oval, increasing 
by insensible gradations of brightness, at first very 
gradually, but at last more rapidly, up to a central 
point, which, though very much brighter than the 
rest, is yet evidently not stellar, but only nebula 
in a high state of condensation. It has in it a few 
small stars ; but they are obviously casual, and the 
nebula itself offers not the slightest appearance to 
give ground for a suspicion of its consisting of stars. 
It is very large, being nearly half a degree long, 
and fifteen or twenty minutes broad. 

This may be considered as a type, on a large 
scale, of a very numerous class of nebulae, of a 
round or oval figure, increasing more or less in 
density towards the central point : they differ ex- 
tremely, however, in this respect. In some, the 
condensation is slight and gradual ; in others great 
and sudden : so sudden, indeed, that they present 
the appearance of a dull and blotted star, or of a 
star with a slight burr round it, in which case they 
are called stellar nebulae ; while others, again, 
offer the singularly beautiful and striking phenome- 
non of a sharp and brilliant star surrounded by a 
perfectly circular disc, or atmosphere, of faint light 
in some cases, dying away on all sides by insensi- 
ble gradations ; in others, almost suddenly termi- 
nated. These are nebulous stars. A very fine 
example of such a star is 55 Andromedse. Eta 
Orionis and Iota of the same constellation are also 
nebulous ; but the nebula is not to be seen without 
a very powerful telescope. In the extent of devia- 
tion, too, from the spherical form, which oval nebulas 
affect, a great diversity is observed : some are only 
slightly elliptic ; others much extended in length ; 
and in some the extension so great as to give the 
nebula the character of a long, narrow, spindle- 
shaped ray, tapering away at both ends to points. 

Annular nebulae also exist, but are among the 
rarest objects in the heavens. The most conspicu- 
ous of this class is to be found exactly half way 
between the stars Beta and Gamma Lyrae, and may 
be seen with a telescope of moderate power. It is 
small, and particularly well defined, so as in fact 
to have much more the appearance of a flat, oval, 



solid ring than of a nebula. The axes of the 
ellipse are to each other in the proportion of about 
four to five, and the opening occupies about half its 
diameter : its light is not quite uniform, but has 
something of a curdled appearance, particularly at 
the exterior edge ; the central opening is not en- 
tirely dark, but is filled up with a faint, hazy light, 
uniformly spread over it, like a fine gauze stretched 
over a hoop. 

Planetary nebulae are very extraordinary objects. 
They have, as their name imports, exactly the 
appearance of planets ; round or slightly oval discs, 
in some instances quite sharply terminated, in 
others a little hazy at the borders, and of a light 
exactly equable or only a very little mottled, which, 
in some of them, approaches in vividness to that of 
actual planets. Whatever be their nature, they 
must be of enormous magnitude. One of them is 
to be found in the parallel of Nu Aquarii, and 
about five minutes preceding that star. Its appa- 
rent diameter is about 20''. Another, in the con- 
stellation Andromeda, presents a visible disc of 
12" , perfectly defined and round. Granting these 
objects to be equally distant from us with the stars, 
their real dimensions must be such as would fill, on 
the lowest computation, the whole orbit of Uranus. 
It is no less evident that, if they be solid bodies of 
a solar nature, the intrinsic splendor of their sur- 
faces must be almost infinitely inferior to that of the 
sun's. A circular portion of the sun's disc, subtend- 
ing an angle of 20", would give a light equal to 
100 full moons; while the objects in question are 
hardly, if at all, discernible with the naked eye. 
The uniformity of their discs, and their want of ap- 
parent central condensation, would certainly augur 
their light to be merely superficial, and in the na- 
ture of a hollow spherical shell : but whether filled 
with solid or gaseous matter, or altogether empty, 
it would be a waste of time to conjecture. 

Among the nebulae which possess an evident 
symmetry of form, and seem clearly entitled to be 
regarded as systems of a definite nature, however 
mysterious their structure and destination, the most 
remarkable are the 51st and 27th of Messier's 
catalogue. The former consists of a large and 



WONDERS OF THE HEAVENS. 



31 



bright globular nebula surrounded by a double ring, 
at a considerable distance from the globe, or rather 
a single ring divided through about two fifths of its 
circumference into two laminae, and having one 
portion, as it were, turned up out of the plane of 
the rest. The latter consists of two bright and 
highly condensed round or slightly oval nebulae, 
united by a short neck of nearly the same density. 
A faint nebulous atmosphere completes the figure, 
enveloping them both, and filling up the outline 
of a circumscribed ellipse, whose shorter axis is 
the axis of symmetry of the system about which it 
may be supposed to revolve, or the line passing 
through the centres of both the nebulous masses. 
These objects have never been properly described, 
the instruments with which they were originally 
discovered having been quite inadequate to show 
the peculiarities above mentioned, which seem to 
place them in a class apart from all others. The 
one offers obvious analogies either with the struc- 
ture of Saturn or with that of our own sidereal 
firmament and milky way. The other has little or 
no resemblance to any other known object. 

The nebulae furnish, in every point of view, an 
inexhaustible field of speculation and conjecture. 
That by far the larger share of them consists of stars 
there can be little doubt ; and in the interminable 
range of system upon system, and firmament upon 
firmament, which we thus catch a glimpse of, the 
imagination is bewildered and lost. On the other 
hand, if it be true, as, to say the least, it seems 
extremely probable, that a phosphorescent or self- 
luminous matter also exists, disseminated through 
extensive regions of space, in the manner of a cloud 
or fog — now assuming capricious shapes, like actual 
clouds drifted by the wind, and now concentrating 
itself like a cometic atmosphere around particular 
stars ; what, we naturally ask, is the nature and 
destination of this nebulous matter ? Is it absorbed 
by the stars in whose neighborhood it is found, to 
furnish, by its condensation, their supply of light 
and heat ? or is it progressively concentrating it- 
self by the effect of its own gravity into masses, and 
so laying the foundation of new sidereal systems or 
of insulated stars ? It is easier to propound such 



questions than to offer any probable reply to them. 
Meanwhile an appeal to facts, by the method of con- 
stant and diligent observation, is open to us ; and, 
as the double stars have yielded to this style of 
questioning, and disclosed a series of relations of 
the most intelligible and interesting description, we 
may reasonably hope that the assiduous study of 
the nebulae will, ere long, lead to some clearer un- 
derstanding of their intimate nature. 

We shall conclude this section by calling the 
reader's attention to a fact, which, if he now learn 
for the first time, will not fail to surprise him, viz. 
that the stars continue visible through telescopes 
during the day as well as the night ; and that, in 
proportion to the power of the instrument, not only 
the largest and brightest of them, but even those of 
inferior lustre, such as scarcely strike the eye at 
night as at all conspicuous, are readily found and 
followed even at noonday, — unless in that part of 
the sky which is very near the sun,— by those who 
possess the means of pointing a telescope accurately 
to the proper places. Indeed, from the bottoms of 
deep narrow pits, such as a well, or the shaft of 
a mine, such bright stars as pass the zenith may 
even be discerned by the naked eye ; and it was 
stated by a celebrated optician, that the earliest 
circumstance which drew his attention to astronomy 
was the regular appearance, at a certain hour, for 
several successive days, of a considerable star, 
through the shaft of a chimney. 



SECTION III. 

Astronomy of the Ancients — Their method of dividing the stars into 
constellations — Constellations easily distinguished — The division 
arbitrary, yet convenient — Anciently was important to the hus- 
bandman — Reason of the names of the constellations — The twelve 
signs of the zodiac — The origin of their hieroglyphic characters — 
Signs and constellations of the same name not coincident — Method 
of studying the stars — Fables, and descriptions of the constella- 
tions — Remarks — The heavenly bodies unequally distant from the 
earth — Earth comparatively but an atom. 

Astronomy seems to have been cultivated as a 
science at a very early age of the world. The sons 
of Seth employed themselves in its study ; and it 



32 



WONDERS OF THE HEAVENS. 



has been asserted on the authority of Berosus that 
Abraham was adroit in celestial observations. In 
Babylon, after its capture by Alexander the Great, 
were found observations on record, that had been 
made by the Chaldeans about one thousand nine 
hundred years previous, which extends back to the 
confusion of tongues. It is probable, therefore, that 
the Chaldeans were the first that cultivated the 
science of astronomy to any great extent. At what 
time they divided the heaven into constellations is 
not known. The method was as follows : they 
fixed one vessel containing water over another that 
was empty, and at the moment a certain star ap- 
peared in the eastern horizon, they opened a small 
passage for the liquid, so that it might run through 
slowly and be caught in the vessel beneath : at the 
moment the same star again appeared in the eastern 
horizon they stopped the flow of the water. This 
quantity of water was then to be divided into 
twenty-four equal parts, and the time one of these 
portions should take to run out was the time 
allowed between the rising of the first and last 
star in any constellation. 

To some of these they gave the names of cele- 
brated individuals, whose memory they wished to 
perpetuate ; to others such birds, beasts, fishes, 
insects, as (if delineated) would occupy the space 
allotted to the constellation. 

If we thus consider a few stars to form a group, 
we may observe this group night after night and its 
shape and appearance will be always the same. 
There are not anywhere in the heavens different 
groups, of considerable extent, so resembling each 
other that an observer can be in any danger of mis- 
taking one for the other. And as the groups can- 
not be mistaken, the individual stars composing 
them may thus be certainly recognised, however 
any single stars in each may resemble each other 
in magnitude, color, and brightness. Being thus 
able to recognise a star which we have once ob- 
served, we may prosecute our observations upon it 
night after night, and year after year. For the 
immediate observations of an individual no more 
than this is requisite ; but when he wants to regis- 
ter their results, or to inform others of their nature, 



it is evident that he can no longer be satisfied with 
this mere power of identifying to his own satisfac- 
tion the particular star which he observes at differ- 
ent times, but he must have some means of dis- 
tinguishing between the different stars which he has 
himself observed, and of announcing to others which 
it is, among all the heavenly bodies, to which he has 
especially applied his attention. For this purpose 
we again have recourse to those groups by which 
we originally distinguished each particular star 
from every other. These groups, when divided for 
the convenience of reference, are called constella- 
tions, (i. e. collections of stars,) a name which is also 
applied to those portions of the heavens which they 
respectively occupy ; and the whole surface of the 
heavens has been long divided in this manner. 
The divisions are arbitrary in themselves, and 
often, perhaps, ill chosen ; but as the only real use 
of them is for the convenience of reference, the one 
important object is to have a single received stand- 
ard ; and it would consequently be very undesira- 
ble to alter them, even for the purpose of making 
what would originally have been a simpler and more 
distinct division. The surface of the heavens being 
thus divided into constellations, consisting each of 
a moderate number of stars, those in each are 
catalogued, and are arranged nearly in the order 
of their apparent brightness. Stars thus registered 
on maps or globes, or their places defined, become 
known bodies, and any astronomer, making obser- 
vations on a particular star, may communicate it to 
any other, who will at once know the star in ques- 
tion, and be able to compare the results with his 
own. Besides, some of the brighter and most re- 
markable stars have been distinguished by particu- 
lar names, which will be given hereafter. 

The number of stars of each magnitude increases 
as their brilliancy diminishes. In the catalogue of 
the Astronomical Society in London, consisting of 
2881 stars, there are but twenty-one above the 
second magnitude ; (three of which are considered 
between the first and second ;) about fifty of the 
second, or between the second and third ; and 
about eighty of the third, or between the third and 
fourth magnitudes. 



r 



WONDERS OF THE HEAVENS 



33 



The division of the starry heavens served to dis- 
tinguish the seasons of the year, and consequently 
the proper periods for the various operations of 
agriculture. Thus the spring signs, or constella- 
tions, were distinguished by those animals which 
were then held in most esteem at that season of the 
year. The first sign they called Aries ; because 
the ram was considered the father of the fleecy 
flock, which afforded them both food and raiment. 
The next sign was named Taurus, because the bull 
was looked upon as being the pride and strength 
of their numerous herds. The last of the spring 
signs was called Gemini, being emblematical of the 
goats bringing forth twins about the season of the 
year that the sun got so high in the zodiac as to 
enter into this constellation. 

The first of the summer signs was called Cancer ; 
because, when the sun entered that constellation, 
he was observed to have attained his greatest 
northern distance fi:"om the equinoctial, and then 
began to assume a retrograde motion. This motion 
the ancients represented under the figure of a Crab, 
because of its creeping backwards. The next con- 
stellation was called Leo, because of the parching 
heat which usually attended the sun's entrance into 
this sign ; and also because the lion, impelled by 
thirst, would frequently quit the sandy desert of 
Zaharah, and make his appearance on the banks of 
the Nile about that time. The last of the summer 
signs was called Virgo ; this constellation the an- 
cients represented under the figure of a virgin, or 
female reaper, holding an ear of corn in her hand ; 
as being emblematical of the harvest time. 

The first of the autumnal signs was called Libra ; 
because when the sun entered into this constella- 
tion he seemed to hold the days and nights in 
equilibrio, giving the same proportion of light and 
darkness to the inhabitants of all parts of the globe. 
The second sign was called Scorpio ; because 
when the sun entered this constellation a great 
variety of fruit was ripened, the immoderate use of 
which was found to be productive of much evil, 
and generally a predisposing cause of fever and a 
numerous train of diseases. Hence the ancients 

represented this sign under the figure of a scorpion ; 
5 



because that reptile gives a poisonous wound with 
its tail to the person who makes too free with it. 
The last of the autumnal signs was called Sagitta- 
rius ; because when the sun entered it the trees 
were nearly divested of their clothing or leaves. 
This they considered as emblematical of the fit 
season for hunting ; and hence represented the 
constellation under the figure of an archer with his 
bow and arrows. 

The first of the winter signs was called Capri- 
cornus, because of the goat, who delighted in climb- 
ing up high and craggy places ; and also as an em- 
blem of the winter solstice ; for when the sun enters 
this sign he begins to ascend or climb higher in the 
zodiac. The next sign was called Aquarius, be- 
cause they observed that when the sun entered into 
this constellation it was always about the wet and 
dreary season of the year ; hence it was represent- 
ed under the figure of a man pouring out water 
from an urn. The next and last of the winter signs 
was called Pisces ; this the ancients represented 
under the figure of two fishes tied back to back, as 
an emblem of the fishing season. 

The constellations thus alluded to are those lying 
in the sun's track, commonly called the twelve 
houses, or signs of the zodiac ; and which bear an 
evident correspondence with the division of the 
year into the twelve parts, called the calendar 
months. 

Besides the above-mentioned twelve, there are 
eighty-one other constellations in the heavens ; 
thirty-four of which are on the north side of the 
equinoctial, and forty-seven on its south side ; 
making in the whole ninety-three constellations. 

Instead of writing the name of the sign of the 
zodiac every time there is occasion to speak of it, 
astronomers use a hieroglyphic or symbol for this 
purpose ; thus °f signifies the Ram ; 8 the Bull ; 
n the Twins ; s the Crab ; SI the Lion ; ri^ the 
Virgin ; ^i the Balance ; n the Scorpion ; t the 
Archer ; vj the Capricorn ; xx; the Water-Bearer ; 
X the Fishes. These symbols were probably 
adopted from some resemblance, fancied or real, to 
the whole or to a part of the animal whose name 
was given to the sign. This may appear the more 



34 



WONDERS OF THE HEAVENS 



credible on an inspection of the accompanying 
plate. 




Thus the horns of the ram have quite a similarity 
in appearance to the symbol °f appropriated to that 
sign in the zodiac. The same resemblance may be 
traced between the head of the bull ; the twins as 
a whole ; the beam of the balance ; the archer's 
weapon ; the whole of the Capricorn ; the stream 
of the water-bearer ; the fishes ; and the hierogly- 
phics used to denote the respective signs named for 
these animals or things. The others, it is true, are 
not so evident, but we may readily suppose that in 
the lapse of many centuries the symbols might be 
somewhat changed from their original form, or we 
might suppose that they originated in the imagina- 
tion of some one whose fancy might be more vivid 
than his eyesight. At any rate the origin thus 
attributed to these characters may serve to amuse 
the reader and to gratify the minds of those who are 
curious on such subjects. 

Hipparchus, who has transmitted us a catalogue 
of the stars known in his time, reckons forty-nine 
constellations, twelve in the zodiac, twenty-two to 
the north of the zodiac, and fifteen to the south. 
And here we would remark that it is necessary to 
distinguish the constellations from the signs of the 
zodiac that have the same name. 

The signs occupy, along the ecliptic, spaces of a 
determinate length, viz. thirty degrees each, while 
the constellations are, on the contrary, scattered, 
in the celestial globe, through regions of very varia- 
ble extent. Besides, owing to the precession of 
the equinoxes, the constellations have moved for- 
ward and are now 30° from the signs of the same 
name. 

The constellation of the Ram, for instance, was 
two thousand years ago in the sign which bears its 



name, or in the first part of the ecliptic, but the 
equinoxes having moved backward about 50'' 
yearly, the sun is now in the constellation of the 
Fishes when it crosses the equator coming north, 
that is, when it is in the sign of the Ram. 

We have seen that space is filled with an infinite 
multitude of stars at an immense distance. These 
myriads of heavenly bodies, which appear to us 
like so many twinkling points, are suns, luminous 
in themselves, the sources of light and heat. It is 
distance alone that renders them so small to our 
imperfect visions. 

We have supposed that the earth is immovable 
in the middle of space ; that the heaven like a 
sphere turns around with a motion rigorously uni- 
form in twenty-three hours fifty-six minutes and four 
seconds upon an imaginary axis nearly invariable : 
half of this sphere the horizon conceals from our 
view. 

The constellations or asterisms have their proper 
names ; whether appropriate or not is nothing to 
the present purpose. We shall give them as we 
find them. It would be almost impossible and al- 
together useless to have given proper names to 
each of the stars. The astronomy of the early ob- 
servers was very rude, as it could not but have 
been. They were satisfied with naming the most 
beautiful stars ; and we have preserved their 
names. But when astronomers wished to study the 
subject with more care, and to distinguish the less 
brilliant of the stars, they could not but perceive 
the imperfection of the earlier method. They fol- 
lowed the course of the naturalist who distributes 
under certain classes a number of individuals. 
Astronomers have distributed the stars into groups, 
around which they have made the outline of some 
animal or fabulous being. Such is, then, the system 
adopted for classing and naming the stars. A lion 
is drawn as an outline for a group ; one star is in 
the neck, another in the back ; this is in the tail ; 
that is in the heart ; and these parts serve to point 
out and distinguish particular stars. 

Next to a beautiful day, what is more imposing 
than a beautiful night ? when the heaven without a 
cloud discovers to us its azure plains, on which 



WONDERS OF THE HEAVENS 



35 



gold seems to mingle its brightness with the dia- 
monds that are scattered over it ! How rich and 
glorious is the mantle of night. In this view she is 
nothing frightful ; she is a goddess : she scatters in 
her path a beneficent dew, that is drank by the 
flowers, the leaves, and the plants, dried by the 
heat of the day ; she mingles with the breezes that 
mild humidity so requisite for vegetation. She 
measures the slumber of nature and spreads a veil 
over man and animals in their repose, which she 
surrounds with a majestic silence. Observe the 
heavens through the whole of a clear night ; those 
of autumn and winter are preferable, because of 
their length. Two clear nights in the months of 
October and March will be suflicient to make you 
acquainted with all the constellations visible at 
this latitude. You will distinguish at first only the 
most brilliant of the stars ; their brightness renders 
them remarkable even when the moon shines. Af- 
ter learning these, they will serve as so many 
marks by which to find the rest. 

Straighten a thread and place it in such a manner 
as to be in a line, or nearly, with three stars, two 
of which are known. On the chart form a similar 
alignment ; this will serve to point out and make 
known to you the unknown star. We must remem- 
ber, however, that lines on the chart will not an- 
swer exactly to those in the heavens. We cannot 
draw a projection of the sphere which shall not 
have disadvantages as well as advantages. Again, 
in consequence of the rotation of the sphere, the 
stars, though they preserve their mutual distances 
and relations, turn with the sphere. The ideal 
lines, therefore, which join them, take different 
directions, that cannot be drawn on the charts. 
Such lines as we imagine to pass through two stars 
are sometimes vertical, at others inclining, and at 
others horizontal. The circumpolar constellations 
especially present remarkable variations of this 
kind. Let the observer place himself in an open 
spot ; let him turn his back to the south ; then, 
having the east on his right and the west on his 
left, he will have before him the northern pole, dis- 
tinguished by a star that appears to be immovable ; 
it is almost the only star of the second magnitude 



in that region, and we shall easily learn to re- 
cognise it. It is sufficient at present to say that all 
the constellations revolve about this point, and in 
the course of twenty-four hours take almost all 
positions : now high, now low ; now on this side, 
now on that. At the same hour of the night the 
aspect of the heavens is different at different sea- 
sons of the year. The horary circle of a star ad- 
vances, day by day, towards the west and towards 
the sun. We could not indicate the place of a star 
without having regard to the daily variations ; for 
its position changes at every instant of the night, 
and it does not return to the same position in less 
than twenty-four hours. 

The figures and the names of the constellations, 
though arbitrary, are connected with each other, 
and with chronology, physics, and mythology. It 
is not without interest to go back to the origin of 
these symbols, and to read in the heavens the 
history of the civil and religious customs of the an- 
cients, who have consecrated their memory in these 
poetic fictions, despised by those only who cannot 
comprehend them. Still it is difficult to give to 
explanations of these figures that character of cer- 
tainty which belongs to positive truth. Many cele- 
brated men have deceived themselves on this sub- 
ject ; many opinions have been adopted lightly and 
defended obstinately. It is more particularly im- 
portant to explain the constellations of the zodiac, 
since they have come to us unchanged through so 
many ages. Their connection with religion and 
history gives them a still greater importance. 

Marks of the same principles are to be found also 
in the other constellations ; but they have suffered, 
in the lapse of centuries, changes, which render 
their interpretation doubtful. It has been well re- 
marked that every thing in Greece is adapted to 
encourage the lover of the arts and to discourage 
the philosopher. It is in the East that we must 
seek the key of those fictions which are based upon 
astronomy. We must study the civil and religious 
usages of that time and place, the natural phe- 
nomena, the seasons devoted to agriculture, &.c. 
We should regard as the work of a people that 
which belongs to them and to them only ; that 



36 



WONDERS OF THE HEAVENS 



which had at a particular epoch a meaning for 
them, and which could have none at any other time 
or to any other nation. 

The heavens have at all times received the 
homage of the people, and the stars, according to 
their importance, have participated in this homage. 
As men always preferred the marvellous to the true, 
the priests took advantage of this disposition to rivet 
their chains, by making science serve as the basis 
of the mysterious emblems they invented. It is 
thus that the truths of nature are bound to fictions 
which disgrace them. 

THE BULL. 

In this cluster are two remarkable groups, the 
Pleiades and the Hyades. According to Hebrew 
authorities this constellation is ascribed to Joseph. 
According to the Greeks it represents the animal 
that carried Europa over the sea from Asia. While 
Europa was gathering flowers, a snow-white bull 
approached her train ; she caressed the beautiful 
animal, and had the courage to sit upon his back. 
He immediately made for the shore, crossed the sea, 
and with the lady arrived safely in Crete. The 
carrying off of Europa and lo by Jupiter is proba- 
bly an allusion to the new year, the sun and moon 
in spring being in the sign Taurus ; and in Virgil 
we find 

The milk-white Bull with golden horns 
Leads on the new-born year. 

The Pleiades were the seven daughters of Atlas 
(the heaven) and of Pleione, (the sea,) or Hesperia, 
(the evening.) Their name seems to be derived 
from a Greek word meaning plurality, they being 
seven ; viz. Electra, Maia, Taygeta, Alcyone, 
Celeno, Sterope, and Merope ; the last of whom 
married a mortal, and her star accordingly became 
dim. Orion was the persecutor of the Pleiades, 
but to save them from his fury Jupiter placed them 
in the heaven, where that giant still pursues them, 
but in vain. 

The Pleiades are sometimes called Virgins of the 
Spring, because the sun enters this cluster in May. 

The Hyades were nymphs of Dodona, daughters 
of Ocean ; they are five in number. Their name 



signifies to rain, because their return announced 
the approach of the rainy season among the an- 
cients. 

The Bull is one of the constellations of the 
zodiac. The head and shoulders of the animal are 
the only parts to be seen ; these are very distinct- 
ly marked. Its declination is about sixteen degrees 
north. It has the Twins on the east, the Ram on 
the west, Orion and the River Po on the south, 
Perseus and the Charioteer on the north. It includes 
one hundred and forty-one stars. In the Pleiades 
there are but seven stars visible to the naked eye, 
and one of these is so dim that it has been called 
the "Lost Pleiad," and has been the cause of many 
beautiful strains of poetry. 

The Pleiades are principally of the fourth and 
fifth magnitudes ; they are situated in the neck of 
the Bull, and form a very conspicuous group, such 
that they cannot be mistaken. The brightest star 
in the group is sometimes called The Light of the 
Pleiades. With a telescope, two hundred stars have 
been discovered in this cluster. 

The Hyades are south-east of the Pleiades, in 
the forehead of the Bull. The five stars of this 
group are so placed as to form the letter V, and 
the most brilliant of these is called Aldebaran ; 
a most important star to navigators, since it is one 
of the nine from which the moon's distance is com- 
puted in the Nautical Almanac. 

ORION. 

Orion was a giant of prodigious size, and an in- 
trepid hunter. His rising in the evening and pre- 
sence during the nights in winter cause to be attri- 
buted to him the power of troubling the ocean. 



Stormy Orion rises. 



ViRG. 



Orion surpassed the rest of mankind in fleetness, 
and boasted that he could overcome all animals. 
A scorpion was sent out of the earth as a punish- 
ment for his boast, and, biting his foot, caused his 
death. He has been called the son of Neptune, 
who gave him power to walk on the water ; others 
have said that he was given by Jupiter, Neptune, 
and Mercury to an inhabitant of Boeotia in the skin 



WONDERS OF THE HEAVENS. 



37 



of a bull ; whence he was placed near that constel- 
lation when advanced to the heavens, and as far as 
possible from the Scorpion. Some suppose the 
fable of Orion intends Abraham entertaining the 
three angels, who foretold the birth of his son 
Isaac. 

Orion is situated to the southward of the Bull. 
It is the most beautiful of all the constellations for 
its extent and the number of its brilliant stars, 
situated in an oblong, four-sided figure, whose 
diagonals are formed by two stars of the first and 
two of the second magnitude. At the north-east 
angle, or in the right shoulder, is Betelgeux, a star 
of the first magnitude. At the south-west angle, 
or in the left foot, is Rigel, of the first magnitude, 
a splendid star. In the middle of the oblong are 
situated three stars of the second magnitude, in an 
oblique line. They have been called The Shoulder- 
belt, The Girdle, The Three Kings, The Rake, Jacob's 
Staff, The Three Stars, because there are no other 
three that resemble them exactly. In Scripture 
they are spoken of' as the bands of Orion : " Canst 
thou loose the bands of Orion ?" To the southward 
of these are several stars of the fourth and fifth 
magnitudes, called The Sword. Both of these were 
named Napoleon in 1807 by" the university at Leipsic, 
but they are more commonly known as the Yard 
and Ell. The three in the belt forming the yard 
measure 'three degrees in length, divided by each 
star into equal parts. The Ell is once and a quarter 
the length of the belt. Orion is represented by the 
figure oft a man, with a club in his right hand, and 
the skin of a lion on his left for a shield ; in the atti- 
tude of assaulting the Bull. Orion is easily dis- 
covered during the beautiful nights of winter. It is 
placed in a part of the heaven which is filled with 
bright stars. About nine or ten o'clock in the 
evening, in February or March, there can be seen 
at the same time as many as twelve stars of the 
first magnitude; viz. Sirius, Procyon, Capella, 
Spica Virginis, Aldebaran, Arcturus, Betelgeux, 
Rigel, Regulus, Denebola, Castor, and Alphard, 
without mentioning a greater number of the second 
magnitude. 

The whole number visible to the naked eye in 



this constellation is seventy-eight; with the tele- 
scope upwards of two thousand have been seen. 

THE HAKE. 

This was an animal which Orion delighted to 
hunt, and its swiftness was one of his attributes ; it 
was therefore placed near him in the skies. It is 
in fact directly against his right leg. It may be 
easily known by means of four stars of the third 
magnitude which form an irregular four-sided 
figure, distinguishing it at once. These stars are 
in the legs and feet of the animal. The principal 
star, marked Alpha, bears about south from the 
middle star in Orion's belt, from which it is distant 
nearly seventeen degrees ; it also bears about west 
from the dogstar, (Sirius,) distance seventeen de- 
grees. The dogstar. Alpha of the Hare, and the 
middle star in Orion's belt form nearly a right- 
angled triangle, Alpha of the Hare being at the 
right angle. 

NOAH'S DOVE. 

This constellation, as is evident from its name, 
commemorates the messenger sent forth by Noah 
from the ark to see if the waters of the deluge had 
abated ; " and the dove returned with an olive 
branch in her mouth." 

" A dove sent forth once and again to spy 
Green tree or ground, whereon his foot may light ; 
The second time returning, in his bill 
An olive branch he brings, pacific sign." 

The Dove is south of the Hare about sixteen de- 
grees, and is nearly on the same meridian with the 
most eastern star in the belt of Orion, distant thir- 
ty-two degrees, and south-west by south of Sirius, 
distant twenty-three degrees nearly. It contains 
one star of the second, one of the third, and two of 
the fourth magnitude. 

THE RIVER PO. 

This river was celebrated by the poets on ac- 
count of the fabled fall of Phaeton, the son of 
Phoebus, from whom he obtained a rash promise 
that whatever boon he asked should be granted. 
No sooner was the promise spoken, than the reck- 



38 



WONDERS OF THE HEAVENS 



less youth, as if bent on his own destruction and 
that of the world, demanded to drive for one day 
the chariot of his father. It was all in vain to re- 
present to him the danger of such an attempt. 
The terrible oath, (by the river Styx,) which even 
the gods could not break, had bound the father ; 
and the son was not to be moved from his purpose. 
Phcebus gave him the reins, which he had no sooner 
received than he betrayed his ignorance and inca- 
pacity to Ihanage them. He had nearly set the 
world on fire, when Jupiter struck him with light- 
ning and tumbled him headlong from his aerial 
flight into the river Po, Some call this constella- 
tion the Nile, or the River of Orion. 

It is a narrow line of stars of the third and fourth 
magnitudes, curving through various parts of the 
heavens. It commences near the left foot of Orion, 
passes westward towards the Whale, where it 
makes a circuit, passes south-east, and again trends 
to the south-west, passing between the Chemical 
Furnace and the Phoenix on the west, and the Clock 
on the east, and finally terminates in the bright 
star Achernar, of the first magnitude ; its entire 
length being about one hundred and thirty degrees. 
It contains eighty-four stars, among which one is of 
the first, one of the second, and eleven of the third 
magnitude. 

THE CHARIOTEER. 

Some suppose that this constellation owes its 
name to Ericthonius, the son of Vulcan and Mi- 
nerva, who was the fourth king of Athens. He 
was of monstrous shape, having the tails of serpents 
instead of legs. Being anxious to conceal his de- 
formity, he invented chariots and the manner of 
harnessing horses to draw them. Others think this 
constellation represents Phaeton, an account of 
whom has been given under the River Po. Others 
think it is Belerophon; others, Absyrtus, the 
brother of Medea; others, Myrtilus, driver of 
CEnomaus. It announces by its heliacal rising the 
entrance of the sun into the Bull. 

The Charioteer is represented by the figure of a 
man in a bending attitude, one foot upon a horn of 
the Bull, with a bridle in his right hand and a goat 



in his left. It is situated eastward of Perseus, and 
north of Orion and the Bull. A line drawn through 
the two most northerly stars in the square of the 
Great Bear will lead to Capella, the principal star 
in the Charioteer. Capella is not only the bright- 
est in this constellation, bul one of the brightest in 
the heavens. The two stars in the shoulders of 
Auriga, with the two in the shoulders of Orion, 
make an oblong, whose length (running north and 
south) is five times its breadth. Also these and the 
star in the right horn of the Bull form two similar 
and nearly equal triangles, the last star being at 
their common vertex. The whole number of stars 
in this constellation is sixty-six. 

THE CAMELOPARD. 

This constellation was so called from an animal 
peculiar to Ethiopia. This animal is very tractable, 
and has the natural properties of the camel, except 
that its body is spotted, whence its name. It was 
made out of the unformed stars which lay between 
Perseus, the Charioteer, the head of the G7'eat Bear, 
and Alruccabah, the north polar star. It contains 
fifty-eight stars, all small. 

THE LYNX 

was made out of forty-four unformed stars lying 
between the Charioteer and the Great Bear. None 
of them are above the third magnitude, and but 
three belong to that order ; the remainder, being 
quite small and scattered, present us nothing very 
interesting or worthy of notice. 

THE TWINS. 

This constellation is a symbol of friendship. 
Some call it Amphion and Zethus; others, Tripto- 
lemus and Jasius ; or Appollo and Hercules ; or, 
lastly, the most common opinion. Castor and Pollux. 
These last were the twin sons of Jupiter and Leda. 
The manner of their birth was remarkable. As 
soon as they had arrived at years of discretion, they 
embarked with Jason in quest of the golden fleece. 
In this expedition both conducted with great 
courage. After their return they cleared the sea 
from pirates ; therefore they have ever since been 



WONDERS OF THE HEAVENS 



39 



considered the friends of navigation. Castor was 
finally killed in battle. Pollux was immortal, and 
as he loved his brother tenderly he entreated Jupiter 
to restore him to life, or take from himself immor- 
tality. Jupiter so far granted the prayer as to 
allow them to share the immortality. This act of 
fraternal love Jupiter rewarded by placing them 
both in heaven under the name of the Twins. 

This constellation is situated to the eastward of 
the Bull, and represents in a sitting posture twin 
brothers, the one holding a lyre in his right hand 
and an arrow in his left, and his head encircled 
with beams of light ; the other holds a club. This 
is the fourth constellation in the zodiac. The sun 
is in the Twins in July. This constellation contains 
eighty-five stars, one (Castor) of the first, and one 
(Pollux) of the second magnitude, in the heads, about 
four and a half degrees asunder ; four of the third 
magnitude, and seven of the fourth. It is easily 
known by means of the two first mentioned. Cas- 
tor is the northernmost and the brightest of the two. 
Pollux is one from which the moon's distance is 
given in the Nautical Almanac. Castor and Alde- 
baran form the base of an isosceles triangle, Capella 
being at the vertex. The constellation forms al- 
most an oblique parallelogram. The relative mag- 
nitude of the two principal stars has undergone 
changes at different periods, and some astronomers 
have thought that Pollux must vary from the first 
to the third magnitude ; but Herschel ascribes the 
variation to Castor, which he found to consist of 
two stars close together, the less revolving about 
the other in three hundred and forty-two years. 

THE LITTLE DOG. 

This is supposed to be one of Orion's hounds 
turned into a constellation, and of course placed 
near him in the heavens. It is sometimes called 
Antecanis, from its rising before the Great Dog. 

Some suppose this constellation represents Anu- 
bis, an Egyptian deity, who had the body of a man 
and the head of a dog. Others say that it is one 
of Actaeon's hounds, that devoured their own mas- 
ter, he havmg been changed into a stag by Diana. 

The Little Dog is south of the Twins. Its princi- 



pal star is Procyon, of the first magnitude. This 
star is situated to the southward of Pollux, distant 
twenty-three degrees, and to the eastward of 
Betelgeux, distant twenty-six degrees. Pollux, Pro- 
cyon and Betelgeux, form a right-angled triangle, 
Procyon being at the right angle. 

Procyon is often used for the name of the whole 
constellation, as Sirius is for that of the Great Dog. 

THE UNICORN. 

This represents an animal about the size and 
shape of the horse, with one white horn growing 
out of the middle of its forehead. It is fabled to 
have existed in Ethiopia. The unformed stars 
which lay between Orion and the Little Dog were 
made into a constellation with this name. It lies 
on both sides of the equator. It contains thirty-one 
stars, a few of them being as large as the fourth 
magnitude; these form a very oblique V, whose 
northerly branch is in a line with the star Xi in 
one foot of the Twins. The remaining stars of this 
constellation are very small and scattered. 

THE GREAT DOG 

Was, with the Dragon, set to watch Europa after 
she had been carried off" by Jupiter. It afterward 
was given to Minos, and at different times belonged 
to Procris, Cephalus and Aurora, and finally to 
Orion. 

Anciently the summer solstice happened while 
the sun was in Capricorn or the Lion. The rising 
of Sirius in the evening or morning announced to 
Egypt the rise of the river Nile, and gave men 
notice, like a faithful dog, to prepare themselves 
against the coming inundation. His name Sirius or 
Siris is derived from Osiris, which means the sun 
and the fertilizing river. 

But the precession of the equinoctial points has 
deprived Sirius of the power of predicting the inun- 
dation. He rose heliacally, that is, before the sun, 
about the 21st of June, fifteen days previous to 
the swelling of the water. It is not visible now in 
that country until the 10th of August. About the 
year 300 of our era, it rose heliacally towards the 
middle of July, and thus announced the season of 



40 



WONDERS OF THE HEAVENS 



great heat and sicknesses consequent, which were 
accordingly attributed to its influence under the 
name of the Dogstar. This was the origin of the 
name dog days, which continue from the 22d of 
July to the 23d of August, during which the sun 
was describing the sign of the Lion or the constella- 
tion of Cancer. 

The Great Dog is to the southward and eastward 
of Orion, and may be easily known by the brilliancy 
of its principal star Sirius, which is the brightest and 
apparently the largest in the heavens, and can never 
be mistaken for any other star. Light, which comes 
from the sun to the earth in eight minutes thirteen 
seconds, or at the rate oi^two hundred thousand miles 
a second, would require three years and eighty-two 
days to pass from Sirius to the earth ; so that if that 
star were destroyed, we should still continue to see 
it more than three years ; and this too is consider- 
ed a.s one of the nearest of the fixed stars. 

Sirius in the Great Dog, Procyon in the Little 
Dog, and Betelgeux in Orion form an equilateral 
triangle. A line drawn from the Pleiades by the 
easternmost star in Orion's belt will lead directly 
to Sirius, which is distant from the belt twenty-two 
degrees nearly. 

THE SHIP ARGO. 

Some think this represents the ship that carried 
Jason and his companions, when they sailed for 
Colchis in quest of the golden fleece. This ship 
had fifty oars, and could not have been much larger 
than our boats ; for it is said that the crew carried 
it on their backs from the Danube to the Adriatic. 
When the expedition was completed, Jason drew 
the ship on shore and consecrated her to Neptune ; 
the poets turned her into a constellation. 

Others imagine this constellation to have been 
formed by the Egyptians, owing its existence to the 
numberless boats of bark which were in use during 
the time of an inundation. The heliacal rising of 
the star Canopus was a precursor of this phenome- 
non, since this star rose with the first of the Lion at 
the summer solstice. 

The ship is situated south of the equator, to the 
eastward of the Great Dog. It may be known by 



the stars in the prow and deck. If a straight line 
joining Sirius and Delta in the Great Dog be pro- 
duced it will reach Zeta in the rowlock. The 
principal star in the constellation is called Canopus, 
which is of the first magnitude, but it never rises 
above our horizon, being in fifty-three degrees south 
declination. There are in the constellation sixty- 
four stars, most of which have so great a southern 
declination that they cannot be seen in the United 
States. 

THE CRAB. 

While Hercules was engaged in destroying the 
famous Lernean monster, Juno sent a sea-crab to 
bite the hero's foot; this new enemy was soon 
despatched, but Juno, to reward its services, placed 
it among the constellations. Sometimes two asses 
are placed in this division of the zodiac, because 
they were the animals Bacchus used to ride, or 
because they assisted Jupiter to overcome the giants, 
terrifying them with their noise. This is the least 
apparent of any constellation in the zodiac, in 
which it is the fifth, lying between the Twins and 
the Lion. Acubens, of the third magnitude, is its 
principal star. A line drawn from Capella through 
Pollux will lead to Acubens ; it is also situated in 
a right line drawn from Bellatrix in Orion to Regu- 
lus in the Lion. The Crab contains eighty-three 
stars. 

Tegmine, the last in the back, is a treble star, 
which requires very favorable circumstances to be 
seen distinctly. 

Prcesepe, the stall, is a small nebula in the breast 
of the Crab, containing five or six stars. 

THE LION. 

The lion was a symbol of strength and power ; 
therefore he was placed where the sun was in mid- 
summer^ thereby signifying the intense heat at that 
time. The Egyptians were annoyed by lions 
during the heat of the summer, as they then left 
the desert and loved to roam by the cool waters of 
the Nile. It was natural, therefore, that they 
should place the lion where we find him. The 
Greeks supposed this constellation to be the Ne- 



Sdstitial 




WONDERS OF THE HEAVENS. 



41 



maean lion, that Hercules slew and Jupiter placed 
among the stars to commemorate the dreadful con- 
flict. The principal star took its name from the Ro- 
man consul, whose valor and virtue have rendered 
his name immortal. In this constellation four stars 
form an irregular four-sided figure. The star in 
the heart is called Regulus or the Lion's Heart, 
that in the tail Dembola. There are ninety-five 
visible stars in the constellation. The south-west- 
ernmost is in, or nearly in the ecliptic, and may be 
distinguished by its brilliancy. A line drawn from 
the north pole-star through the Pointers passes 
about twelve degrees east of Regulus. It is one of 
the nine stars from which the distance of the moon 
is measured, to obtain the longitude at sea. To 
the northward of Regulus, eight degrees distant, is 
a star of the second magnitude ; near these are five 
other stars of the third magnitude ; the whole form- 
ing a cluster resembling a sickle, Regulus being in 
the extremity of the handle. The other stars will 
be easily found in the heavens after one has found 
Regulus and Denebola, and observed their relative 
situation to the rest on the map. These two are 
important, being often used to point out other 
clusters in their neighborhood. 

THE LITTLE LION. 

This constellation was made by Hevelius out of 
the unformed stars situated between the Lion on the 
south and the Great Bear on the north. It contains 
fifty-three stars, all of them small ; the principal 
one, being of the second magnitude, is situated in 
the body of the animal. 

THE SEXTANT 

Was formed out of the stars unformed by the an- 
cients, situated between the Lion on the north and 
the Water Snake on the south. It contains forty- 
one small stars. It was formed in honor of the 
nautical instrument called Hadley's quadrant. 

THE WATER-SNAKE AND THE CUP. 

This Cup is said to be the same from which 

Jupiter, Neptune, and Mercury drank when they 

were kindly entertained by a peasant of Boeotia. 
6 



The gods were so pleased with his hospitality, 
that they placed his cup as a constellation in the 
heavens. The Water Snake was a monster that 
infested the vicinity of lake Lerna. It had a hun- 
dred heads, and as soon as one was cut off two 
grew out in its place, unless hot iron were applied 
to the wound. It was one of the labors of Hercules 
to destroy this monster. 

The Cup contains thirty-one stars, one being of 
the third magnitude and called Alkes, distant from 
Alphard twenty-five degrees in an east-south-east 
direction, and from Denebola south by west thirty 
degrees. It may be known by a crescent formed 
by several stars of the fourth magnitude. 

The Water-snake contains sixty stars, most of 
them small. It trends to the eastward in a ser- 
pentine manner from the Little Dog to the Balance, 
lying south of the Crab, the Lion and the Virgin. 
Its principal star is Alphard, called also the Heart, 
which is twenty-three degrees distant from Regulus, 
south-south-west. It may be distinguished by its 
dark reddish appearance. The head of the Snake 
may be recognised by four stars of which the upper 
three form an arch. When the head is on the 
meridian the tail is far below the horizon ; and its 
whole length cannot be traced out in the heavens 
until the Cup is on or near the meridian. 

THE GREAT BEAR. 

Calisto, an attendant and favorite nymph of 
Diana, was changed into a bear by Juno. To pre- 
vent her being injured by the hunters Jupiter trans- 
ferred her to heaven, placing her among the con- 
stellations. Juno, furious, besought Thetis to forbid 
the Bear dipping into the ocean, which it never does 
in our latitude. 

According to another account, the two Bears 
are the nymphs who fed Jupiter on mount Ida. 
They are called Helices, because of their motion 
round the pole. The ancients represented this 
constellation by a wagon ; hence it has been called 
Charles' Wain or Wagon. This constellation never 
sets in our latitude, and consequently takes all 
positions in passing round the pole. It is formed 
principally of seven beautiful stars, four of M^hich 



42 



WONDERS OF THE HEAVENS 



form an oblong; the other three are in a curved 
line; of these, the two first are in the continuation 
of the diagonal. These seven stars are sometimes 
called the Dipper and sometimes the Plough. When 
on the meridian above the pole, the bottom of the 
Dipper lies toward us, the handle on the right. 
The two stars most distant from the tail are called 
the Pointers, because a straight line drawn through 
them and continued would strike the pole-star 
nearly. The distance of the nearest Pointer, called 
Dubhe, from the pole is twenty-nine degrees; the 
distance between the Pointers is five degrees. 

The right fore-paw and the two hind-paws are 
severally distinguished by a couple of stars of the 
fourth magnitude ; these six are the only stars in 
this constellation that ever set in this latitude. 
On the side opposite the tail, there are six or seven 
stars of the fourth magnitude, placed in a semicircle 
convex toward the oblong ; these, with three or four 
of the Lynx, form an S, and are in the head of the 
Bear. This constellation has always been an ob- 
ject of observation, being so conspicuous and con- 
stantly visible. All nations seem to have been 
equally , attracted by its appearance. It is even 
asserted that the Iroquois Indians have given it 
the same name as the ancients did ; though there 
is really no resemblance to a bear in the constella- 
tion. The star near the root of the tail, called 
Megrez, is in the equinoctial colure. 

The whole number of stars in this constellation 
is eighty-seven. One is of the first, three are of 
the second, seven of the third magnitude. 

BERENICE'S HAIR. 

Berenice was the daughter of Philadelphus and 
Arsinoe. She married Ptolemy Euergetes and 
loved him with much tenderness. He went on an 
expedition against his enemies, and Berenice, being 
anxious for his safety, vowed to dedicate her hair 
to the goddess of Beauty if her husband should re- 
turn safe. She performed her vow on the victori- 
ous return of Euergetes, but the day after the locks 
had disappeared from the temple. Conon an as- 
trologer Avas sent for ; and when the king expressed 
great regret for the loss of what he so much valued. 



and inquired of Conon what had become of them, 
the astrologer, to make his court to the monarch, 
artfully pointed to some unformed stars and ex- 
claimed " there are the queen's locks." The king 
was pleased and the queen's vanity flattered by 
this reply, and Conon publicly reported that Jupi- 
ter had taken the queen's hair from the temple and 
placed it among the constellations. 

It is a beautiful constellation of very small stars, 
situated quite near each other, and between Dene- 
bola and Charles' Heart. It contains forty-three 
stars, one being of the fourth magnitude. The 
stars are so small that it is not always easy to per- 
ceive them. Yet it is not possible to mistake any 
other group for them. 

THE CROW. 

Apollo had occasion for the services of the crow. 
He performed his part so faithfully, that as a re- 
ward, he was transferred to a place among the 
stars by the god of day. 

Some say that this cluster took its name from the 
daughter of Coronoeus, who v.'as changed into a 
crow for her own safety. This constellation is 
situated to the southward of the Virgin and to the 
eastward of the Cup, and is distinguished by means 
of four stars of the third magnitude which form a 
trapezium. Its principal star is called Algorab, 
distant from Alkes in the Cup twenty-two degrees 
in a direction north-easterly, and from the Sheaf of 
the Virgin fifteen degrees south-westerly. It in- 
cludes nine visible stars, four being of the third, 
and one of the fourth magnitude. 

THE VIRGIN. 

The Virgin, an emblem of justice and law, repre- 
sented Themis, whose balance is at her feet, or 
Astraea, the daughter of Jupiter and Themis, 
whom the crimes of men obliged to abandon earth 
for heaven at the end of the golden age. 

Faith flies and piety in exile mourns, 

And justice, here oppressed, to heaven returns. 

Astraea was placed among the constellations of the 
zodiac under the name of Virgo. 

Some consider Virgo as Ceres and the emblem 



— 



WONDERS OF THE HEAVENS 



43 



of harvest ; or Diana of Ephesus ; or Isis of Egypt ; 
or the great god^iess of Syria, Atergatis; or For- 
tune ; or Cybele, drawn by lions ; or Minerva, the 
mother of Bacchus; or the sibyl of Virgil, who 
with a golden branch in her hand conducted Eneas 
into the lower regions; or Erigone, the death of 
whose father by the hands of some intoxicated 
peasants caused her so much grief, that in a fit of 
despair she hung herself, and was placed among 
the constellations of the zodiac. Her faithful dog 
Moera, afterward placed in the heavens, directed 
her to the spot where her father was buried. The 
Virgin is the seventh constellation of the zodiac; it 
is east of the Lion, and between the Crow and Be- 
renice's Hair. It is of considerable extent, and 
contains one hundred and ten stars, one being of 
the first, one of the second, five of the third, and 
ten of the fourth magnitude. The longest diagonal 
of the trapezium of the Great Bear being produced 
toward the south will strike a star of the first mag- 
nitude in the Virgin; this is the Sheaf of Wheat, 
(Spica Virginis.) It forms also an equilateral tri- 
angle with Arcturus and the star in the tail of the 
Lion. A right line from this last to the Sheaf 
would nearly bisect a right angle formed by five 
stars of the third magnitude in the Virgin, one side 
of which angle is directed toward Regulus and lies 
along the ecliptic, the other side is directed toward 
th-e last star in the tail of the Great Bear. Spica 
may be known by its solitary splendor, there being 
no star very near it of any magnitude. The situa- 
tion of this star in the heavens has been determined 
very accurately for the assistance of seamen. The 
moon's distance from it is taken to determine the 
longitude. It lies within the moon's path, and two 
degrees south of the earth's orbit. A star of the 
second magnitude, called Vindemiatrix, is situated 
in the right arm, half way between Spica and Be- 
renice's Hair. Regulus, Vindemiatrix and Charles' 
Heart, form nearly a right-angled triangle, Vinde- 
miatrix being at the right angle. Two stars, Eta 
and Zeta, of this constellation point out the direc- 
tion of the equator. Several other stars of the 
third magnitude lie scattered about in this constel- 
lation, which may be easily traced on the map. 



BOOTES AND THE GREYHOUNDS. 

Bootes or the Bear-driver represents Areas, the 
son of Jupiter and Calisto. Juno, jealous of Jupiter 
for his partiality to Calisto, transformed her to a 
bear, and Areas, who was a famous hunter, one 
day started a bear in the chase, and not knowing 
that it was Calisto, his mother, was on the point of 
killing her, when Jupiter, to prevent the deed, 
transported them both to heaven and made constel- 
lations of them. 

Bootes has also been considered as Icarus, whom 
Bacchus taught the art of making wine. He im- 
prudently gave some to the peasants, who, thinking 
it pleasant, drank it to excess and became intoxi- 
cated ; then conceiving they had been poisoned by 
Icarus, they killed him. Some say, however, that 
it is Atlas, who supports the world, because former- 
ly its head was near the pole. Volney thought that 
Bootes was Osiris. 

The Greyhounds, named Asterion and Chara, ac- 
cording to fable, are the hounds with which Bootes, 
through mistake, hunted his mother Calisto; they 
are represented as being in pursuit of the Great 
Bear, which Bootes is hunting round the north pole, 
he holding in his right hand the leash with which 
the hounds are fastened together. 

The Bear-driver is represented as a huntsman 
grasping a club in his left hand. It is situated to 
the eastward of Charles' Heart and west of the 
Northern Crown. It contains fifty-four stars, of 
which one is of the first and seven of the third 
magnitude. 

This constellation may be found by means of its 
principal star, Arcturus, which shines with a lustre 
and hue very much like Mars. Arcturus is near 
the right knee, and is about the same distance east 
as Capella is west of the southernmost Pointer. It 
is also in a straight line which passes through the 
two last in the tail of the Great Bear, and in the 
upper base of the trapezium of the Lion produced. 
In Bootes is a pentagon north-east of Arcturus. 
The upper hand of the figui'e, formed by several 
stars of the fourth magnitude, is near the tail of the 
Great Bear. 

The Greyhounds, a constellation formed by He- 



44 



WONDERS OF THE HEAVENS 



velius out of stars left unformed by the ancients, 
lies between Bootes and the Great Bear, and con- 
tains twenty-five stars, most of which are of the 
fifth and sixth magnitude. Charles' Heart, the 
principal star, of the third magnitude, in the neck 
of the southern Hound, Chara, was so named in 
memory of Charles the first, by Scarborough. This 
star, with Alioth in the Bear and the southernmost 
Pointer, forms a right-angled triangle, the vertex 
of the right angle being at Charles' Heart. A line 
drawn through it and Alioth will lead to the pole- 
star. When Alioth and Charles' Heart are in the 
same vertical circle, they will be on or near the 
meridian. 

THE CENTAUR AND THE CROSS. 

An imaginary existence, half man and half horse. 
Under the reign of Ixion, of Thessaly, a herd of 
wild bulls laid waste that country and rendered 
the mountains inaccessible. The king promised a 
reward to whomsoever would destroy or drive them 
from his kingdom. Some young men, having found 
means to break and ride horses, pursued and de- 
stroyed the bulls. The peasants, seeing them at a 
distance, conceived, as the Mexicans did in later 
times, that the men and the horses were one 
animal, or rather monsters of a dreadful form. The 
celebrated Chiron was one of the centaurs. 

This constellation is south of the Virgin, and the 
whole of it does not rise in this latitude ; it is far 
south, occupying a large space in that hemisphere. 
In it are thirty-five stars, two being of the first and 
one of the second magnitude. The principal of 
these are not visible in this latitude. The star in 
the east shoulder may be seen in June about twelve 
or fourteen degrees above the horizon. There is 
no other star of equal brightness in its vicinity ; it 
may therefore be easily distinguished. It is nearly 
on the same meridian with Arcturus. In the other 
shoulder, and almost exactly south of the Sheaf, is 
a star of the fourth or fifth magnitude. A few de- 
grees north of these two, in the shoulders, are four 
small stars in the head of the constellation, resem- 
bling those in the head and shoulders of Orion, in 
their relative position. 



Between the legs of the Centaur is that beauti- 
ful constellation, which has been so much cele- 
brated and admired by those who have visited a 
southern latitude. The Cross. It is said to repre- 
sent the cross which Constantine the Great saw in 
the sky when going to give battle to Maxentius, 
whom he totally defeated, near Rome. Yet this 
constellation is not visible at Rome, its declination 
being too far south to allow it to rise above the 
horizon in that latitude. It is formed of four stars 
situated in the milky-way. The bright star in the 
top of the cross is nearly south of Algorab in the 
Crow, and distant from it about forty-one degrees, 
and south-west of the Sheaf, distant forty-seven de- 
grees. 

THE WOLF. 

This constellation is said to have been Lycaon, 
an Arcadian monarch, celebrated for his wickedness 
and inhumanity. The sins of mankind had become 
so enormous, that Jupiter visited the earth to punish 
impiety. He came to Arcadia, where the people 
began to pay adoration to his divinity. Lycaon, 
however, to try him, served up human flesh on his 
table. For this wickedness Jupiter immediately 
destroyed Lycaon's house and turned its owner into 
a wolf. This animal is represented as pierced with 
an arrow from the bow of the Centaur. The an- 
cients regarded' the constellation of the Wolf as an 
unlucky presage, as they also did the Serpent and the 
Scorpion, which occupy neighboring regions of the 
heavens, and are symbols of the winter. There is 
another origin given to this constellation, viz. 
Romulus and Remus being thrown into the Tiber, 
and floating ashore, were found and protected by a 
wolf, until Faustulus carried them away and educa- 
ted them as his own. 

The Wolf is situated eastward of the Centaur and 
south of the Balance, and has such a high southern 
declination that but few of its stars are visible in 
this latitude. 

It contains twenty-four stars, three being of the 
third and three of the fourth magnitude, the bright- 
est of which may be seen in a clear evening just 
above the horizon. 



WONDERS OF THE HEAVENS 



45 



THE BALANCE. 

Two thousand years ago the sun at the time of 
the autumnal equinox was in the Balance, which 
was represented as placed either in the hands of 
the Virgin or the claws of the Scorpion. The 
Greeks, whose sphere was like that of the Chalde- 
ans, had but eleven constellations in the zodiac. 
They gave the Scorpion an extent equal to two 
signs, by prolonging the claws into what is now the 
Balance. The sign filled by the claws was called 
ChelcR. The Balance was formed first by the 
Egyptians, as their monuments prove. As Augus- 
tus was born in September, flattery leagued with 
astrology to celebrate the blessing promised to the 
world by his birth. They replaced the Balance, 
the symbol of justice, in heaven. Bearing this in 
mind, the following lines from Virgil, addressed to 
Augustus, will be easy to interpret. 

And seated near the Balance, poise the days 
Where in the void of heaven a space is free, 
Between the Scorpion and the Maid, for thee ; 
The Scorpion, ready to receive thy laws. 
Yields half his region and contracts his claws. 

The Balance is the eighth constellation in the 
zodiac from the vernal equinox, and is east of the 
Virgin. It may be known by means of four bright 
stars, forming a four-sided figure ; the most south- 
westerly of these is in the ecliptic. Three other 
stars in this cluster form an isosceles triangle, the 
two brighter of which distinguish the two scales of 
the Balance. In the cluster are found fifty-one stars, 
two of the second, two of the third, and twelve of 
the fourth magnitude. 



THE SERPENT-BEAEER 
SERPENT. 



AND THE 



The Serpent-bearer was so named by the an- 
cients, who represented it under the figure of a 
man with a large beard, holding in his hand a staff", 
around which was wreathed a serpent ; or as holding 
with both his hands a serpent, which is writhing 
under the power of his grasp. The serpent was 
sacred to Ophiucus, and was the symbol of medi- 
cine, and of the god who presided over it. Ophiu- 
cus is but another name for ^sculapius, the son of 
Apollo and Coronis, or Arsinoe, one of the Hyades ; 



this fable alludes to the circumstance of the Ser- 
pent-bearer's rising when the sun, being in the 
Bull, sets. Some add that the Serpent-bearer was 
fed by a goat and brought up by Chiron, the cen- 
taur ; and in reality the Centaur rises just before 
the Serpent-bearer, which happens at the setting of 
Capella, (the Goat.) Ophiucus is considered by 
some as Jason ; by others as Tantalus. The River 
Po sets at the rising of Ophiucus ; and from this 
circumstance the fable had its origin, that the 
water constantly flies before the thirsty Tantalus. 
The serpent placed in the hands of Ophiucus is an 
emblem of his wisdom and sagacity, or, as some 
think, of his skill in curing the bite of the serpent. 
Again, the Serpent is said to be Cadmus, who im- 
plored the gods to change him into that reptile, to 
save him from the constant and malignant persecu- 
tions of Juno, 

The Serpent-bearer occupies a considerable 
space in the heavens. It is situated to the south- 
ward of Hercules, and contains seventy-four stars. 
In the head is Ras Alhague, the principal star, of 
the second magnitude ; it is situated to the left and 
south of the star in the head of Hercules. Farther 
south are two stars of the third magnitude, very 
near each other, forming the eastern shoulder. In 
the western shoulder are also two stars near to- 
gether, of the fourth magnitude ; these are to the 
right of the heads oV Hercules and Ophiucus; which 
being connected, together with those in the shoul- 
ders, by right lines, will make a trapezium, at the 
southern point of which is a thick cluster of little 
stars forming the letter V, open toward the north. 
This beautiful cluster is the head of the Royal Bull, 
or the Bull of Poniatowski. South of the trapezium 
may be seen in the folds of the Serpent a quadrila- 
teral, formed by stars of the fourth magnitude. 
The tail of the Serpent is between two trapezia, 
those of Ophiucus, and Antinous, near the Eagle. 
North-west of the head of Ophiucus, and south of 
the Crown, is the head of the Serpent, which forms 
a letter Y placed obliquely, the tail of which is 
broken, as it were, and curved. In this curve is 
situated the principal star of the Serpent, Unukal- 
hay, or the Heart, being of the second magnitude. 



46 



WONDERS OF THE HEAVENS 



This may also be known by means of a small star, 
just north of it. The tail of the Y is prolonged by a 
row of stars of the third magnitude, which extends 
far below the equator. The serpent terminates 
near the constellation of the Eagle. 

THE NORTHERN CROWN. 

This cluster represents a crown presented by 
Bacchus to Ariadne, the daughter of Minos, king of 
Crete. Bacchus loved her with much tenderness, 
and after her death transferred the crown to the 
heavens, placing it among the constellations. 

He bids her crown among the stars be placed, 
As an eternal constellation graced. 
The golden circlet mounts, and as it flies 
Its diamonds twinkle in tlie northern skies. 

This constellation may be easily known by means 
of its circular form, which resembles a wreath, con- 
sisting of six stars. It is situated to the eastward 
of Bootes and north of the Serpent's Head, and con- 
tains one star of the third magnitude, called Al- 
phacca, which is in the middle of the diadem, 
eleven degrees east of Mirac in Bootes. A line 
drawn from Vindemiatrix through Arcturus will 
lead close to Alphacca. The two last, with 
Seginus, form an isosceles triangle, whose vertex is 
at Arcturus. In this cluster there are twenty-one 
stars, of which only six or eight are visible to the 
naked eye. 

THE LITTLE BEAR. 

As the Great Bear represents Calisto, so does 
the Little Bear her dog. But it is more probable 
that the latter was named long after the former, and 
took its name from the general similarity discovera- 
ble in the appearance of the two. 

This constellation, though not remarkable in its 
appearance, and containing but few conspicuous 
stars, is justly distinguished from all others for the 
peculiar advantages which its position in the hea- 
vens is well known to afford to nautical astronomy, 
and especially to navigation and surveying. 

Situated near the celestial pole, the stars in this 
group appear to revolve about it, very slowly, and 



in circles so small as never to descend beflow the 
horizon. 

In all ages of the world, this constellation has 
been more universally observed, and more careful- 
ly noticed, than any other, on account of the impor- 
tance which mankind early attached to the position 
of its principal star. 

This star, which is so near the true pole of the 
heavens, has, from time immemorial, and, as it 
were, by common consent, been denominated the 
North Polar Star. 

The Little Bear contains twenty-four stars, in- 
cluding three of the third magnitude and four of the 
fourth. The seven principal stars in this constella- 
tion are so situated as to form a figure very much 
resembling that in the Great Bear, only that the 
Dipper is reversed, and about one half the size of 
the larger one. 

The first of these, in the handle, called Cynosure, 
or Alruccaba, is the polar star, round which the 
rest are constantly revolving. The two last in the 
bowl of the Dipper, corresponding to the Pointers in 
the Great Bear, are of the third magnitude, situated 
about fifteen degrees from the pole, the brightest 
of which is called Kochab, Avhich signifies an axle 
or hinge, probably in reference to its moving so 
near the axis of the earth. 

Kochab may easily be known by its being the 
brightest and middle one of three conspicuous stars 
forming a row, one of which is about two degrees 
from Kochab, and the other three degrees. The 
two brightest of these are situated in the breast and 
shoulder of the animal, about three degrees apart, 
and are called the Guards or Pointers of the Little 
Bear. They may be seen at all hours of the night. 

Of the four stars which form the bowl of the 
Dipper, one is so small as hardly to be seen. They 
lie in a direction towards Gamma in Cepheus; but 
as they are continually changing their position in 
the heavens, they may be much better traced out 
from the map than from description. 

Kochab is distant from Benetnasch about twenty- 
five degrees, and from Dubhe about twenty-four, 
and hence forms with these two very nearly an 
equilateral triangle. 



WONDERS OF THE HEAVENS 



47 



THE SCORPION. 

The Scorpion was the symbol of maladies and 
destructive plagues. When the sun entered this 
constellation a great variety of fruit was ripe, by 
an immoderate use of which sickness was brought 
on, a predisposition to fever and a numerous train 
of diseases. Hence the ancients represented this 
sign under the figure of a scorpion, because that 
reptile inflicts a poisonous wound. It was the 
terror of Orion, Phaeton, and Hyppolitus, This 
constellation was anciently represented by other 
symbols, but most commonly by a Scorpion, 

Ovid says that this is the Scorpion that at Juno's 
command appeared (rising from the earth) and 
stung Orion, who died of the bite. They were re- 
moved to the heavens, but placed as far as possible 
from each other. 

The Scorpion is a beautiful group of stars, and 
easily found ; it contains forty-four stars, one being 
of the first, one of the second and eleven of the 
third magnitude, and is distinguished for the pecu- 
liar lustre and position of its principal stars. It is 
situated to the eastward of the Balance. Its princi- 
pal star is Antares, the heart of the Scorpion. 
This is a remarkable star, being of a reddish hue, 
and the most brilliant of any in that region of the 
heaven. It forms, with two others of the fourth 
magnitude, a very obtuse angle, (say one hundred 
and seventy degrees,) Antares being at the vertex. 
This star is distant from the Sheaf of the Virgin 
forty-six degrees, direction east-south-east. It is 
one of the stars from which the moon's distance is 
measured, to find the longitude. It is distant from 
Zubenelgin, the north scale of the Balance, about 
twenty-five degrees, in a south-easterly direction. 
The tail of the Scorpion trends to the southward 
till it reaches the fourth star from Antares; here 
it turns to the eastward, continuing to the sixth 
star, whence it trends northward; thus forming 
a circular line of stars, of the third and fourth mag- 
nitudes, in which the principal is named Lesath, 
in the extremity, distant eighteen degrees from 
Antares, in a south-east by south direction. This 
circular line of stars, forming the tail of the Scorpi- 
on, is very conspicuous, and may be easily traced. 



HERCULES AND CERBERUS. 
Hercules was the son of Jupiter and Alcmene, 
and one of the most renowned heroes of antiquity. 
He performed many wonderful exploits, commonly 
called the "labors of Hercules." He put on a 
poisoned tunic, which had been presented him, 
through the treachery of the centaur Nessus ; no 
sooner had he done so, than he felt a fatal fire 
through all his bones and the blood boil in his veins. 
As the distemper was incurable, he built a funeral 
pyre, laid upon it his club and the skin of the 
Nemaean lion, and setting fire to it, he was con- 
sumed. Jupiter looked from heaven and promised 
the surrounding gods that he would raise to the 
skies the immortal parts of a hero who had cleared 
the earth from so many monsters and tyrants. 

High o'er the hollow clouds the coursers fly, 
And lodge the hero in the starry sky. 

The twelfth, last, and most difficult of his labors 
was to bring upon earth the three-headed dog 
Cerberus, stationed by Pluto at the mouth of hell to 
prevent the living from entrance and the dead from 
escape. Hercules dragged off" the treble-headed 
monster, and Jupiter placed him in the same con- 
stellation with Hercules. 

This constellation is represented by a man partly 
covered with a lion's skin, in a kneeling posture, 
the feet toward the north pole, the head to the 
south, and near that of the Serpent-bearer. The 
three-headed dog, Cerberus, is in his left hand, 
and a club in his right. The cluster is situated 
south of the Dragon and west of the Harp. It oc- 
cupies a large space in the heaven, and the figure 
is in an inverted position. The principal star is 
Ras Algethi, in the head. A line drawn from Vega 
in the Harp to Alpha in the Crown traverses a 
quadrilateral in the body of Hercules, one of whose 
diagonals continued will reach Ras Algethi, which 
may be also known by its proximity to Ras Alhague, 
in the head of the Serpent-bearer, being five degrees 
west-north-west of it. About half way from Ras 
Algethi to the Crown are two stars of the third 
magnitude, three degrees apart, in the west shoul- 
der. The most northerly of these is named Ruti- 
licus. In the east shoulder are also two stars of 






48 



WONDERS OF THE HEAVENS. 



the fourth magnitude. These pairs, with Ras Al- 
gethi, form a triangle nearly equilateral. 

THE DRAGON. 

Some affirm to be the monster that Cadmus slew, 
when he was in search of his sister Europa. His 
father Agenor, king of Phenicia, ordered him to 
bring his daughter home or never return himself 
Having sent his companions to a neighboring grove 
to bring water, their long delay either wearied or 
alarmed him. He therefore went to the spot and 
found a dragon feeding on their remains. He in- 
stantly attacked, and with the assistance of Mi- 
nerva, overcame the monster. Others assert that 
in a war with the giants this dragon was brought 
into the combat and opposed to Minerva, who 
seized it in her hand and hurled it into heaven, 
around the axis of the sphere, before it could un- 
wind its folds, and that it sleeps there to this day. 

But the more commonly received fable was, 
that this constellation represented the dreadful 
monster that guarded the golden apples in the gar- 
den of the Hesperides. Hercules killed the dragon 
and carried away the fruit; but Juno, as a reward 
for its faithful services, changed the monster into a 
constellation. 

This important group is of the number of those 
which do not set in our latitude. It is easily re- 
cognised by a line of stars with three coils. The 
tail commences near the back of the Gi^eat Bear; 
the third star from its extremity is of the second 
magnitude, and is between the guards of the Little 
and the tail of the Great Bear. This star is called 
by navigators the Dragon's Tail. It was also once 
the Polar star, having been nearer the pole than 
even the Cynosure is now. Following their line 
of stars, we soon reach a curve at Theta; then a 
coil, containing Eta and Zeta ; then come two stars 
and another coil, in which are three stars of the 
third magnitude ; now, taking a direction toward 
Hercules, another coil and the head may be found. 
In this coil are five or six stars, one being of the 
fourth magnitude. The head may be distinguished 
by means of five stars, forming an angle, (the vertex 
being in the nose,) or the letter V, the point to- 



ward the west, the opening toward the east. The 
brighter star in the head is called Rastaben. It is 
nearly east from the last star in the tail of the 
Great Bear. Rastaben is interesting fi:-om its con- 
nection with the discovery of a new law in physical 
science. 

THE HARP. 

This small cluster takes its name fi*om the instru- 
ment which Apollo, the god of music, gave Orpheus. 
With this the musician played in such a masterly 
manner that the most rapid rivers stayed their 
course, the savage beasts were overcome, the 
mountains moved and forests bent to listen to the 
melody. After his death Orpheus received divine 
honors, the muses gave an honorable burial to his 
remains, and his lyre became one of the constella- 
tions. This cluster of stars has been sometimes 
represented as an eagle flying downward ; also 
called the Falling Vulture. 

It is situated south-easterly firom the head of the 
Dragon. It contains the most brilliant star in the 
northern hemisphere, called Vega. This, with 
Arcturus and the pole star, forms a large triangle, 
Vega being at the vertex of its right angle. As 
regards the pole, Vega is opposite Capella. A 
little south of Vega are three stars of the third 
magnitude, which form an isosceles triangle. Vega 
is south-east of Rastaben about fifteen degrees. 
The Harp contains twenty-one stars, one being of 
the first and three of the third magnitude. 

THE ARCHER. 

Chiron, a centaur, son of Saturn, was famous for 
his knowledge of music, medicine and shooting. 
He instructed the greatest heroes of his age. To 
jEsculapius he taught medicine, to Apollo music, to 
Hercules astronomy. He was wounded in the 
knee by an arrow from the bow of Hercules, when 
he pursued the centaurs and they fled for protec- 
tion to Chiron. The arrow had been dipped in the 
blood of the Lernean hydra, and consequently the 
wound was incurable ; he therefore implored Jupi- 
ter to take away his immortality, that death might 
free him from the excruciating torments he endured. 



Ef[u(irni 




Equator ! 




WONDERS OF THE HEAVENS 



49 



His prayers were heard, and Jupiter turned him 
into the constellation of the Archer. This constel- 
lation is situated to the eastward of the Scorpion, 
and is easily distinguished by means of several stars 
of the fourth magnitude, which form a figure bear- 
ing some resemblance to the Plough in the Great 
Bear. This, being on the confines of the milky- 
way, is sometimes called the Milk-dipper. The 
constellation occupies a considerable space in the 
southern hemisphere, containing a number of con- 
spicuous stars. The whole number of its visible 
stars is sixty-nine, five being of the third and ten 
of the fourth magnitude. There is also a curve line 
of stars like a bow, convex toward the Scorpion ; 
the arrow is formed by these stars. Of the two 
stars close together in the upper end of the bow, 
the brightest, which is of the fourth magnitude, 
serves to point out the winter solstice, being about 
two degrees north of the tropic of Capricorn, and 
less than one east of the colure. 

THE EAGLE AND ANTINOUS. 

This was originally one constellation, the Eagle 
or Egyptian Hawk, who carried the thunderbolts 
of Jupiter, as a reward for having nourished him in 
a cave of Crete, where he was concealed to prevent 
his becoming the food of his father Saturn. By 
others it is supposed to be Merops, king of the 
island of Cos, this monarch having been transform- 
ed into an eagle and placed among the stars. 

The dismemberment of this constellation was the 
work of the emperor Adrian. Antinous was a 
young man from Bythynia, of whom the emperor 
was so fond that at his death he built a temple to 
his memory, and endeavored to propagate a belief 
that his favorite had become a constellation and 
was placed near the Eagle. Antinous is also call- 
ed Ganymede, a beautiful youth, who was carried 
off by Jupiter under the shape of an eagle and made 
his cupbearer. 

South of the Fox and Goose, and north of the Ar- 
cher, may be seen three stars near each other, and in 
an oblique line. Of these the middle is Altair, in 
the Eagle, of the first magnitude ; the most southerly 
is in the head of Antinous, and the most northerly 



in the back of the bird. These two last are of the 
third magnitude. There are two stars of the third 
magnitude in the tail and two in the southern wing. 
South of the Eagle are four stars which form a 
quadrilateral ; this is the upper part of Antinous. 
One of them, that in the shoulder, is the variable 
star Eta. It is about eight degrees southerly from 
Altair, and is one of those stars which often change 
their appearance. Altair in the Eagle is an impor- 
tant star, being one of those from which the moon's 
distance is given. By the situation and brilliancy 
of this star the constellation may easily be found. 
It contains seventy-one stars ; one of the first, nine 
of the third, and seven of the fourth magnitude. 

THE DOLPHIN. 

Bacchus when young was found asleep in the 
island of Naxos by some pirates of Tuscany, who 
captured and carried him off". Finding himself 
their prisoner when he awoke, he soon made them 
repent of their rashness. He first filled the boat 
with ivy, and afterward drove them into the sea 
and changed them to dolphins, transferring to 
heaven, as a constellation, Acestes, the pilot, be- 
cause he alone had expressed some sympathy for 
the prisoner. 

Another account is, that this cluster represents 
the Dolphin who persuaded Amphitrite to become 
the bride of Neptune, though she had previously 
made a vow of perpetual singleness. For his 
services on this occasion the Dolphin was placed 
by Neptune among the stars. 

A small lozenge or rhombus, formed of four 
stars, of the third magnitude, very near together, 
makes it easy to find this constellation, which is 
situated about fourteen degrees north-east by east 
of the Eagle, and exactly south of the principal star 
in the Swan, called Deneb, of the first magnitude, 
and distant from it about thirty degrees. The 
rhombus is called by many " Job's Coffin," without 
any known reason for the name. There is a fifth 
star in the body of the Dolphin, a little south of the 
rhombus. There are beside several very small 
stars in the cluster, only visible under favorable 
circumstances. 



50 



WONDERS OF THE HEAVENS 



THE SWAN. 
As of many other constellations, so of this, 
several fables are told respecting its origin. Or- 
pheus, when torn in pieces by Bacchanalians, was 
transformed to a Swan and placed in heaven near 
the Harp. Jupiter changed himself to a swan on 
an occasion when it suited his purpose. Accord- 
ing to some this constellation took its name from 
Cycnus, a son of Neptune, who was invulnerable, 
so that, to destroy him in battle, Achilles threw 
him and attempted to smother him, but he was 
suddenly changed to a swan. Ovid says that 
Cycnus, a relative of Phaeton, who deeply lament- 
ed the fate of that insensate, and of his sisters, 
who wept themselves to death, was changed into a 
swan. 

Forth from his sides the wings and feathers grow ; 
Forth from his mouth proceeds the blunted beak ; 
And Cycnus now into a swan is turned. 

The Swan is situated to the eastward of the Harp, 
and is remarkable for forming a large cross in the 
milky-way, down which the bird is flying with out- 
spread wings. As regards the pole, this cluster 
is opposite that of the Twins. The cross in the 
cluster is formed by stars of the third magnitude in 
the head, body, and wings of the bird ; one of them 
is, however, of the first magnitude, called Deneb. 
It is at the top of the cross, in the body of the bird; 
the beak being the foot of the cross, where there is 
a star of the third magnitude, named Albireo. This 
constellation contains eighty-one stars, one being 
of the first, six of the third, and twelve of the fourth 
magnitude. There have been discovered in the 
Swan three variable stars. One of these, situated 
about midway of the neck, was first observed to be 
variable in 1686. Its changes are completed in a 
little more than a year. The star near the junction 
of the neck with the body varies from the third to 
the sixth magnitude. Its changes are not regular ; 
they seem to require ten years or more for their 
completion. The third variable star is in the head. 
It was seen in the summer of 1670, appearing 
then of the third magnitude, was scarcely visi- 
ble in October, became brighter than ever in the 



spring of 1671, and disappeared finally in the spring 
of 1672. 

CAPRICORN. 

This is said to be a goat, that was brought up 
with Jupiter on mount Ida. He discovered the 
conch shell and blew upon it ; thus carrying terror 
into the ranks of the Titans in their war against 
heaven. In one attack the gods, affrighted, con- 
cealed themselves under the forms of different 
animals ; Mercury became an ibis, Apollo a crane, 
Diana a cat, Jove a ram, Juno a cow, and finally 
Pan, plunging into the Nile, became a Capricorn; 
that is, the part of his body above the water took 
the form of a goat, that beneath the form of a fish. 
Or this constellation may represent Amalthsea, who 
fed Jupiter on goats' milk, and who was rewarded 
for her kindness by being placed among the stars. 
Jupiter gave a horn to one of the nymphs that had 
taken care of his helpless years. This was the 
horn of plenty, a talisman to give the possessor what- 
ever she might desire. Capricorn is situated to the 
eastward of the Archer. A line, drawn from Vega 
to Altair, and produced, will reach two stars very 
near together in the head of this constellation. Of 
these the more northerly is a double star, and is 
distant from Altair twenty-three degrees nearly, in 
a south-south-east direction. To the southward of. 
this, and distant about two and a half degrees, is a 
star marked Beta; this at sea is called the south 
head of Capricorn. Both are of the third magni- 
tude. Nearly east from these is another pair of 
the third magnitude; these are in the tail. The 
whole number of stars is fifty-one, most of them 
small and inconspicuous. 

ANDROMEDA. 

Was the daughter of Cepheus and Cassiopeia. Cas- 
siopeia had the vanity to boast that she was more 
beautiful than the Nereids, who were so piqued at 
the boast that they persuaded Neptune to send a 
sea-monster to lay waste the country. To free him- 
self from this monster Cepheus was obliged to expose 
his daughter, which he accordingly did by chaining 
her to a rock on the sea-shore. The gods, struck 



WONDERS OF THE HEAVENS 



51 



with the sufferings of so much innocence and beau- 
ty, sent Perseus to deliver her, Perseus, possess- 
ing the head of Medusa, which was fabled to 
change into stone any living thing that looked upon 
it, delivered the lady and married her. 

This constellation is situated to the southward of 
Cassiopeia, and to the westward of Perseus. It is 
represented by a woman having her arms extended 
and chained to a rock. In the head of Andromeda 
is a star of the second magnitude, named Al- 
pheratz. This star is on an imaginary line drawn 
from the north-eastward in the square of the Great 
Bear through the north polar star, and distant from 
the latter about sixty-one degrees. In a north- 
easterly direction from Alpheratz, at the distance of 
about fifteen degrees, is Mirach, a star in the girdle 
of Andromeda. In the same direction nearly, and 
distant about thirteen degrees from Mirach, is Al- 
maach, a star in the foot. From this last Algol, in 
the head of Medusa, is about thirteen degrees, and 
in an easterly direction. Almaach, Algol, and 
Algenib (in Perseus) form very nearly a right-angled 
triangle, the right angle being at Algol. Mirach, 
Almaach, and Algol divide into three equal parts 
the space between the head of Andromeda and the 
centre of Perseus. Andromeda when on the meri- 
dian is directly over our heads. It contains sixty- 
six stars, three being of the second and two of the 
third magnitude. 

THE FISHES, 

According to some, are those whose form Venus 
and Cupid assumed to escape the giant Typhon. 
Others say that two fishes, having found an egg, 
rolled it on shore, where it was warmed by a dove, 
and from it there arose Astarte, the Venus of As- 
syria. From that time the Assyrians abstained 
from eating fish. According to Theon the Fishes 
are the children of the Southern Fish, after whom 
they always rise. 

This constellation occupies much space in the 
heavens. It is represented by two fishes tied 
together, yet quite distant from each other, the 
connecting cord being long and undulating. Both 
of the fishes join the Flying Hmse, one being east 



and the other south, quite close to the wing. The 
first, which may be called the Eastern Fish, is ex- 
actly south of Merach in Andromeda. The cord 
may be traced in a south-easterly direction till we 
reach Alpha, which is in the knot. From Alpha 
the cord runs north-westerly, until it reaches the 
Western Fish, between which and Alpha in the knot 
are three stars of the fourth or fifth magnitudes, 
nearly equidistant from each other. The Fishes 
contain one hundred and thirteen stars, most of 
which are very small. 

CEPHEUS, 

A king of Ethiopia and one of the Argonauts, 
made a constellation after death. Although he 
had promised Andromeda to Phineas, yet when 
Neptune flooded the country and Andromeda was 
devoted as food for a sea-monster, Cepheus was 
ready to comply with the demand of Perseus, who 
promised to save the lady if she would marry him. 
Their nuptials were' opposed by Phineas, but his 
opposition ceased when Perseus held before his eyes 
the Gorgon's head. 

Cepheus is represented with a crown on his head 
and a sceptre in his hand. He is opposite the Great 
Bear with regard to the pole. His head is in the 
milky-way, and may be known by three stars of the 
fourth magnitude in the crown, forming a little 
triangle. The principal star in the constellation is - 
named Alderamin; it is of the third magnitude, 
situated in the west shoulder, forming a quadrila- 
teral, that may be readily distinguished, with three 
other stars of the fourth magnitude, of which one 
is in the girdle, one in the east arm, and one in the 
east knee. Alderamin bears east by north from 
Rastaben in the Dragon, being distant about twenty- 
nine degrees. It is about twenty-eight degrees 
from the pole star, and twenty-six from Schedir, 
a bright star in Cassiopeia, in a west-north-west 
direction. 

CASSIOPEIA, 

Or the lady in her chair, was the wife of Cepheus 
and mother of Andromeda. As a reward for her 
hard- wrung consent to sacrifice her daughter for 



52 



WONDERS OF THE HEAVENS 



the good of the country, she was carried to heaven 
after death and placed among the constellations by 
Minerva. 

Cassiopeia holds in her hand a branch of the 
palm tree. Her head and body are in the milky- 
way, and her foot rests upon the polar circle. She 
is surrounded by her husband, daughter, and son- 
in-law. This constellation is midway between An- 
dromeda and the pole. It is visible at all hours of 
the night in our latitude, being in such high north- 
ern declination that it never sets. It contains fifty- 
five stars, five being of the third magnitude, which 
form (as many persons imagine) the figure of an 
inverted chair. Beta is in the back of the chair. 
It is the western star of the bright cluster. The 
uppermost of these is in the breast, and is named 
Schedir. The situation of Beta is important to 
mariners; it is used for finding the latitude, and 
for determining the variation of the needle of the 
compass fi^om the true north. Beta also serves 
to mark a spot memorable as the situation of a 
lost star. 

In November, 1572, a star was seen about five 
degrees from Beta, which became suddenly so 
brilliant that it surpassed the planets in brightness, 
and could be seen in the daytime. This brilliancy 
diminished until 1573, when it became entirely in- 
visible. Its color exhibited the appearances of 
flame. It was first of a dazzling white, then of a 
reddish yellow, and lastly of an ashy paleness, in 
which its light expired. Some imagined that it 
would reappear after one hundred and fifty years, 
but it has not been seen since. Vince, one of the 
most learned astronomers of the age, has remarked, 
that the disappearance of stars may be the destruc- 
tion of that system, at the time appointed for the 
probation of its inhabitants ; and the appearance of 
new stars may be the formation of new systems for 
new races of beings, then called into existence to 
adore their Creator. The conflagration (if so it 
were) was visible for sixteen months. How tre- 
mendous must it have been to be visible so far ! La 
Place says " that the supposition of such a con- 
flagration on the surfaces of some of the stars is 
confirmed by their change of color." 



THE FLYING HORSE AND THE LITTLE 
HORSE. 

The flying horse is Pegasus, who sprung from 
the blood of Medusa, when Perseus cut off" her 
head. Pegasus fixed his residence on mount Heli- 
con, where, by striking the earth with his hoof, he 
produced the famous fountain called Hippocrene. 
Pegasus was long the favorite of the muses, but, 
being tamed by Neptune, he Avas given to Bellero- 
phon to assist him in subduing the fiery monster 
Chimaera. 

After the destruction of Chimfera, Bellerophon 
attempted to fly to heaven on Pegasus, which so 
incensed Jupiter that he sent a fly to sting the 
horse ; this occasioned the fall of the rider, but the 
horse continued his upward flight and became a 
constellation. 

The Little Horse was named by the ancients, 
who supposed that it was the brother of Pegasus, 
named Celeris, a horse given to Castor, who was 
skilful in the management of those animals. The 
head only of the Little Horse is visible in the hea- 
vens. 

The Flying Horse is situated between the Swan, 
the Dolphin, and the Eagle on the west, Andromeda 
and the Eastern Fish on the east, and occupies a 
large space in the heavens. It may be known by 
means of four stars of the second magnitude, form- 
ing a large four-sided figure, called the square of 
Pegasus. Alpheratz, the north-easternmost star 
of the square, is in the head of Andromeda; to the 
southward of this, and distant about fourteen de- 
grees, is the star Algenib; to the westward of Al- 
genib, distant about sixteen degrees, is the star 
Markab ; to the northward of Markab, distant about 
thirteen degrees, is Scheat, from Avhich to Alphe- 
ratz is about fifteen degrees, direction westerly. 
These are the four stars that form the square of Pe- 
gasus. Markab is one of the nine stars from Avhich 
navigators measure the distance of the moon. In 
Pegasus there are eighty-nine stars ; most of them, 
however, are small. We see but a part of the Fly- 
ing Horse ; the poets imagined that the rest was 
hid in the clouds. 

About twenty degrees from Markab, in a wester- 



Equal or 




£(|natoj 




\ 




WONDERS OF THE HEAVENS 



53 



ly direction, is a star in the nose of the Little Horse, 
named Enif. The cluster contains ten stars, of 
which the four principal are of the fourth magni- 
tude, rather noticeable on account of the figure 
they form than for their brilliancy. They form a 
long irregular square, the two in the nose being 
much nearer together than those in the eyes. This 
horse, like Pegasus, is in an inverted position. 

THE WAT.ER-BEARER. 

This is Ganymede, whom Jupiter, under the form 
of an eagle, carried off to be the cupbearer of the 
gods. The hoof of Pegasus rises just before the 
stream of the Bearer. The water represents the 
fountain Hippocrene, which Pegasus produced by a 
blow of his hoof The nine stars of the Dolphin 
are the nine muses who drink at the fountain. 
Some consider the Water-bearer as Deucalion, who, 
escaping with his Avife Pyrrha from the flood, land- 
ed on mount Parnassus, the abode of the muses, of 
Pegasus, and of Hippocrene. 

The Water-bearer is situated to the southAvard of 
Pegasus. Within it are four stars, so situated as 
to form the figure of a Y, very plainly visible; 
these stars are in the hand of the Bearer and the 
handle of the Urn. This figure is distant from 
Markab in Pegasus about eighteen degrees, in a 
direction south-west by south, and Avith the Dol- 
phin and the head of the Capricorn forms an 
isosceles triangle. To the Avestward of the Y and 
distant about four and a half degrees, is a star of 
the third magnitude, named Alpha, in the east 
shoulder of the Bearer ; it is the principal star in 
the constellation. A line draAvn from Alpheratz, 
in the head of Andromeda, through Markab, Avill 
lead directly to Alpha. Two stars, one in the east 
hand, the other in the Avest shoulder, form with 
Alpha a triangle, the largest angle being at Alpha. 
About eighteen degrees from the Y, in a south by 
east direction, is Scheat, of the third magnitude, 
in the right leg. This cluster contains one hun- 
dred and eight stars, four being of the third magni- 
tude. The stream or cascade terminates in the 
mouth of the Southern Fish, Avhich is thirty degrees 
south of the Y. 



THE SOUTHERN FISH 
Is said by the Assyrians to have saved the life of 
Derceto, and by the Egyptians the life of Isis. 
Fomalhaut, its principal star, by its rising at night 
indicated that the sun was in the solstitial Lion, as 
Sirius did by rising heliacally. These two stars 
Avere Avorshipped by the Egyptians, who considered 
them as the causes of the Nile's inundations. 
Fomalhaut Avas honored under the name of Phagrus 
or of Dagon. His presence above the horizon at 
that time showed the shortest night of the year; 
for it rose at evening and set in the morning at the 
summer solstice. 

This constellation lies south of the Water-bearer ; 
it is represented as a fish drinking the water flow- 
ing from the urn. There is in it one beautiful star 
of the first magnitude, Fomalhaut, in the mouth. 
A line drawn from Scheat and passing through 
Markab (both in Pegasus) will lead to Fomalhaut. 
It is one of the stars from which the moon's distance 
is measured, and consequently its place has been 
determined Avith great precision. The cluster con- 
tains tAA^enty-four stars, one being of the first, tAVO 
of the third, and five of the fourth magnitude. 

PERSEUS AND THE HEAD OF MEDUSA. 

Perseus Avas the son of Jupiter and Danae. 
Polydectes, king of one of the Cyclades, where 
Perseus lived, ordered him to cut ofiE" the head of 
Medusa and bring it to the palace. Vulcan gave 
the hero a casque that rendered him invisible, and 
a famous sword, Mercury lent him his wings and 
talaria, and Minerva a shield. He attacked the 
Gorgons, Avhose hair was stiff" with snakes, and cut 
off" the head of Medusa. As he flcAV off" Avith this 
trophy of success, the blood that dropped fi'om it 
on the sandy deserts of Lybia become serpents 
innumerable, Avhich have infested that desolate 
►country ever since. 

The gory drops distilled, as swift he flew, 
And from each drop envenomed serpents grew. 

Perseus after death became a constellation, and 
the head of Medusa was placed near him. 

This constellation is principally in the milky- 
way. It is represented by a man having wings to 



54 



WONDERS OF THE HEAVENS. 



his feet, a sword in his right hand, and a trunkless 
head in his left. It is situated north of the Plei- 
ades, west of the Wagoner, and east of Andromeda. 
Perseus is easily known by means of three stars of 
the second and third magnitudes, which form an 
arc of a circle, the concave being toward the Great 
Bear. The middle star is Algenib, of the second 
magnitude. South of this arc is Algol, in the head 
of Medusa, surrounded by a group of very small 
stars ; west from Algol are two stars near together ; 
these are in the leg of Perseus, near the knee; 
south of these is one in the foot ; these three form a 
curve. Algol is the only star at all remarkable in 
the head of Medusa. It is usually very bright, but 
changes from the second to the fourth magnitude in 
three and a half hours, and back again in the same 
time; then it remains visibly the same for two 
days, when the same changes begin again. 

This constellation contains fifty-nine stars, of 
which number about a dozen are in the head of 
Medusa. When Algenib and Algol are near the 
meridian the most beautiful part of the heaven is 
visible. Its glories are magnificent beyond descrip- 
tion, and he who looks upward at this time can 
scarcely fail "to reverence the Being who made 
the seven stars and Orion." 

THE RAM. 

Phryxus and Helle, obliged to fly from their step- 
mother's cruelty, were carried on a winged ram 
with a golden fleece across the Hellespont, in which 
Helle fell and perished. Phryxus arrived at Col- 
chis, and sacrificed the animal to Mars. The story 
of the expedition of the Argonauts relates to the 
sun (at the equinox) in the Bull. From Thrace, 
the country of Jason, they saw the sun rise in the 
direction of Colchis. The Ram, rising just before 
it, was an emblem of a golden fleece, guarded by a 
monster, (Cetus,) and by a Bull, that vomited flame. 
At evening, Ophiucus, that is, Jason, rises from the 
spot whence the Ram rose in the morning. The 
hero then has carried off" this precious fleece. His 
companions, Plercules, Castor, Pollux, and Ce- 
pheus are at the horizon. 

The Ram is the second constellation in the 



zodiac, being situated next east of Pisces It is 
north of the head of the Sea Monster, (Cetus,) and 
west of the Bull. It may be distinguished by the 
stars in the head. Of these there are three ; the 
two brightest being of the second and third magni- 
tudes, four degrees apart, one in each horn. That 
in the right horn is named Arietis, and is the princi- 
pal star, and an important one, being of the number 
of those from which the moon's distance is mea- 
sured at sea; that in the left horn is called Beta. 
To the southward of this is a star in the ear, named 
Mesarthim, of the fourth magnitude. The other 
stars are small. The cluster contains sixty-six 
stars, one being of the second, one of the third, 
and two of the fourth magnitude. 

THE SEA MONSTER. 

The delineation of this constellation being as 
little like a whale as Pollonius' cloud, it may be 
better to call it as above. It represents the monster 
sent to devour Hesione, which was killed by Hercu- 
les, or that sent to destroy Andromeda, which was 
killed by Perseus. 

South of the Ram we shall find a star of the 
second magnitude ; it is Menkar, in the jaw of the 
monster. It forms an equal sided triangle with the 
Ram and the Pleiades. The five stars in the head 
form a pentagon. South-west of this pentagon is a 
star in the lower jaw, and six degrees farther, in 
nearly the same direction, is the wonderful star of 
1596, named Mir a, which changes from a star of 
the second magnitude so as to become invisible in 
about three hundred and thirty-two days ; though 
Hevelius is certain that it once disappeared for four 
years. From Mira south-east we shall find a 
quadrilateral formed by four stars of the third mag- 
nitude. Still farther south-east is Deneb, in the 
tail, of the second magnitude. South-west of the 
quadrilateral we find in the fore paw another very 
small quadrilateral. 

We have thus endeavored to describe the most 
important of the constellations, their position and 
that of their individual stars, that no one may be at 
a loss to find them in the heaven, should his taste 



WONDERS OF THE HEAVENS. 



55 



fortunately lead him to the study of so important 
and interesting a subject. We have given the 
fables of the ancients respecting them, in hope to 
attract those who are not yet interested, and, in a 
few instances, given explanations of the origin and 
even reasonableness of these fables; being of the 
number of those who think that the stories of anti- 
quity, which appear to some the productions of 
childish folly or imbecile superstition, were replete 
with meaning, hidden, to be sure, from the common 
people, but full of wisdom to the sage, although the 
simification of most of them has been lost. The 
meaning of the few may teach us what to think of 
the rest. 

In the serious contemplation of so many splendid 
luminaries, the mind will have its reasoning facul- 
ties expanded and filled with more sublime ideas of 
the grandeur, the magnificence, and the unlimited 
extent of creation; nor can it fail to be inspired 
with reverential delight in reflecting on the wisdom 
of those immutable laws that govern the stupendous 
whole, and preserve such wonderful harmony, con- 
nection, and order throughout so many systems of 
systems. It will wander beyond the reach of con- 
tracted prejudice, and, rising above this orb on 
which the body rests, feel conscious of the exist- 
ence of other suns, and soar, unfettered by the 
chains of superstition, through thousands of millions 
oft revolving worlds. 

The stars appear to be fixed in the concave of a 
large sphere. This appearance is not caused by 
the stars being situated at equal distances from us, 
but is an illusion of vision; the narrowness of hu- 
man sight not permitting us to see, in their true 
places, objects that are very remote. 

This will appear evident when we consider that 
the sun and the moon appear to be placed in the 
same concave and equidistant, while in fact the sun 



is four hundred times farther off than the moon, and 
the stars at a distance infinitely greater than the 
sun ; we know not how far ! It may be inferred 
from this that the stars are at unequal distances, 
and that there may be as great a distance between 
two that appear to us close to each other, as 
between our sun and that star which is nearest 
him. 

The rays of light reflected by the atmosphere 
produce that bluish tint, which forms the beautiful 
celestial shade commonly called the azure sky. If 
this were not an appearance only, but a reality, 
and the stars were attached to it, they would not 
be more than forty-five miles distant; for beyond 
this it is probable the atmosphere is too rare to re- 
flect the rays. Instead of this being the distance 
of the stars, it is so great as to be entirely beyond 
the comprehension of the human mind; so great 
that all other considerations of remote or high 
seem to vanish from the mind in its endeavors to 
contemplate it. We may think of space as 

Without bound, 
Without dimensions, where length, and bread h, and height, 
And time, and place are lost. 

Our earth then, compared to the whole of creation, 
is less than an atom floating in a sunbeam. This 
must be granted when it is understood, that comets 
travel millions upon millions of miles from the 
farthest of our planets, and at such immense dis- 
tances, must be still nearer to the sun than to any 
of the stars ; otherwise would they be attracted by 
those stars and return not again to our system. 

Take thy boldest flight 
Amid those sovereign glories of the skies, 
Of independent native lustre, proud, 
The souls of systems ! What behold'st thou now ? 
A wilderness of wonders burning round ; 
Where larger suns inhabit higher spheres ! 
And ask for Him who gave these orbs to roll. 



CHAPTER II. 



SECTION I. 

Erroneous notions derived from appearances — \Vhy the stars are not 
visible to the naked eye in the day-time — Fictions of poetry re- 
specting the universe — Is the earth its centre? — Does the earth 
rotate ? — Different constellations visible at different regions — Ro- 
tation of the earth consistent with appearances — Permanence of 
its axis — Precision of the ancients — Discovery by Copernicus — 
Causes of erroneous impressions — Consequences of considering 
the earth immovable — Centrifugal and centripetal forces — Pendu- 
lum a means of finding the force of attraction — Measures of 
gravity — Attraction not a simple force — Effects of the earth's 
rotation — Trade winds — Proofs of wisdom in the rotation of the 
earth — Consequences of a changeable axis — Advantages of the 
existing law of attraction — Perturbations periodical. 

Man, misled by appearances, regarded for a long 
time the earth as nearly a plain, situated in the 
middle of the universe ; the sun, the moon, and 
the stars were all in motion around it. 

As evident as this hypothesis may appear to the 
untutored eye, we shall see by an attentive obser- 
vation of various phenomena that it is altogether 
erroneous. 

If one of our senses is strongly affected it ceases 
to be sensible to slight impressions. A low sound 
cannot be readily heard in the midst of loud and 
confused noises. The eyes, acted upon by a bril- 
liant light, can perceive nothing situated in a dark 
corner. But by degrees they become accustomed 
to the shade, and recover slowly the faculty of dis- 
tinguishing objects. 

The cause is similar that deprives us of the sight 
of the stars during the brightness of day. They 
are as much within view as ever, but it is only by 
twilight that they successively become visible, be- 
ginning with the most brilliant and the most east- 
erly. The moon produces the same effect upon 
the small stars near it as the sun does upon all of 
them. Some appear to describe small circles 
without ever setting or going beneath the horizon, 
and are lost to our sight only because morning 
approaches to diminish their splendor; but the 
greater number describe more extended curves ; 
they disappear beneath the horizon, and after some 



hours reappear in the opposite region of the hea- 
vens. They must therefore, while below our hori- 
zon, continue the curves which they describe while 
above it. 

It has been found that the stars apparently 
describe around the earth circumferences parallel 
to each other and oblique to our horizon, by a 
rotation that is uniform and accomplished in the 
same time by each. These appearances lead men 
to regard the earth as immovable in the centre of 
a celestial sphere, whilst this sphere turns round 
with a uniform motion, carrying with it all the 
stars, fixed, like so many twinkling points. We 
shall by and by come to explain the falseness of 
this supposition, which, however false it is, will 
give us some good idea of the movements of the 
heavens. 

Placed upon the earth, it does not seem, to us as 
a sphere isolated in space. An attentive observa- 
tion, however, will convince us that if we had the 
power of removing to a distance from the globe, it 
would present to our sight the same form as the 
sun and moon present, with apparent dimensions 
differing at different distances. Reason has dissi- 
pated the mist of ancient physics, and with it have 
vanished the fictions and brilliant illusions of poesy. 

The earth is no longer "a plain, supporting a 
celestial dome;" Phebus no longer "extinguishes 
his brilliant fire in the waves ;" Sol rises without 
" Aurora's opening the gates for his flaming 
chariot ;" and, finally, Olympus is no longer a 
" small mountain of Thessaly, inhabited by the 
fabled god of thunder." 

This first step it was not very difficult to take. 
But is the earth fixed in the centre of the universe ? 
Does the universe revolve about it ? Are the mul- 
titude of heavenly bodies attached to the surface of 
a sphere turning on one of its diameters ? It is not 
always the first step that is the most difficult. Ob- 
servations did not correct this opinion. The sport 
of deceitful appearance, it was necessary, if we 



WONDERS OF THE HEAVENS. 



57 



would escape this error, to put aside prejudices 
born with us, and which our eyes confirmed at every 
look, instead of removing. The philosopher who 
first affirmed that the celestial sphere was motion- 
less, and that on the contrary the earth turned 
round, dared to contradict the testimony of the 
senses. It was by the comparison of different 
phenomena, by studying their consequences, that 
he discovered those great natural laws, whose im- 
press is upon every thing around us. 

First, it was observed that the moon, and the 
planets Venus and Mercury, sometimes passed over 
the sun ; all these heavenly bodies at times covered 
the stars in the same way as a cloud conceals them. 
They are then at unequal distances from the earth. 
It is also probable that the stars are at unequal dis- 
tances, since they have very different degrees of 
splendor and apparent magnitude, for " one star 
differeth from another in glory." There are my- 
riads which are not visible to the naked eye, and 
of whose existence we should be wholly ignorant 
but for the telescope. Is it not probable that these 
are more distant than the others ? 

We are under the necessity of choosing between 
two suppositions, either of which explains well 
enough the facts observed. One (that which agrees 
better with the testimony of our senses) supposes 
the heavens to revolve around us with a general 
and equable motion ; the other, which is the only 
reasonable one, supposes the earth to revolve on 
its axis, while the celestial sphere remains motion- 
less. 

A traveller, shifting his locality on our globe, 
will obtain a view of celestial objects invisible from 
his original station, in a way which may be not 
inaptly illustrated by comparing him to a person 
standing in a park close to a large tree. The 
massive obstacle presented by its trunk cuts off" his 
view of all those parts of the landscape which it 
occupies as an object ; but by walking round it a 
complete successive view of the whole panorama 
may be obtained. Just in the same way, if we set 
off" from any station, and travel southward, we shall 
not fail to notice that many celestial objects which 
are never seen from that station come successively 



into view, as if rising up above the horizon, night 
after night, from the south, although it is in reality 
our horizon, which, travelling with us southward 
round the sphere, sinks in succession beneath them. 
The novelty and splendor of fresh constellations 
thus gradually brought into view in the clear calm 
nights of tropical climates, in long voyages to the 
south, is dwelt upon by all who have enjoyed this 
spectacle, and never fails to impress itself on the 
recollection among the most delightful and interest- 
ing of the associations connected with extensive 



^ 



^ 
* 



* 



* 



■¥- 



M 



^ 



^ 



^ 




^ 



travel. A glance at the accompanying figure, ex- 
hibiting three successive stations of a traveller, 
A, B, C, with the horizon corresponding to each, 
will place this process in clearer evidence than any 
description. 

Suppose the earth itself to have a motion of rota- 
tion on its centre. It is evident that a spectator at 
rest (as it appears to him) on any part of it, will, 
unperceived by himself, be carried round with it : 
unperceived, we say, because his horizon will con- 
stantly contain, and be limited by, the same terres- 
trial objects. He will have the same landscape 
constantly before his eyes, in which all the familiar 
objects in it, that serve him for landmarks and 
directions, retain, with respect to himself or to each 
other, the same invariable situations. The perfect 
smoothness and equality of the motion of so vast a 
mass, in which every object he sees around him 
participates alike, will prevent his entertaining any 
suspicion of his actual change of place. Yet, with 
respect to external objects, — that is to say, all 



58 



WONDERS OF THE HEAVENS 



celestial ones which do not participate in the sup- 
posed rotation of the earth, — his horizon will have 
been all the while shifting in its relation to them, 
precisely as in the case of our traveller. Recurring 
to the figure, it is evidently the same thing, so far 
as their visibility is concerned, whether he has been 
carried by the earth's rotation successively into the 
situations A, B, C ; or whether, the earth remain- 
ing at rest, he has transferred himself personally 
along its surface to those stations. Our spectator 
in the park will obtain precisely the same view of 
the landscape, whether he walk round the tree, or 
whether we suppose it sawed off, and made to turn 
on an upright pivot, while he stands on a project- 
ing step attached to it, and allows himself to be 
carried round by its motion. The only diiference 
will be in his view of the tree itself, of which, in 
the former case, he will see every part, but, in the 
latter, only that portion of it which remains con- 
stantly opposite to him, and immediately under his 
eye. 

By such a rotation of the earth, then, as we have 
supposed, the horizon of a stationary spectator will 
be constantly depressing itself below those objects 
which lie in that region of space towards which the 
rotation is carrying him, and elevating itself above 
those in the opposite quarter ; admitting into view 
the former, and successively hiding the latter. As 
the horizon of every such spectator, however, ap- 
pears to him motionless, all such changes will be 
referred by him to a motion in the objects them- 
selves so successively disclosed and concealed. In 
place of his horizon approaching the stars, there- 
fore, he will judge the stars to approach his hori- 
zon ; and when it passes over and hides any of 
them, he will consider them as having sunk below 
it or set; while those it has just disclosed, and 
from which it is receding, will seem to be rising 
above it. 

If we suppose this rotation of the earth to con- 
tinue in one and the same direction, — that is to say, 
to be performed round one and the same axis, till 
it has completed an entire revolution, and come 
back to the position from which it set out when the 
spectator began his observations, — it is manifest 



that every thing will then be in precisely the same 
relative position as at the outset: all the heavenly 
bodies will appear to occupy the same places in 
the concave of the sky which they did at that in- 
stant, except such as may have actually moved in 
the interim ; and if the rotation still continue, the 
same phenomena of their successive rising and 
setting, and return to the same places, will con- 
tinue to be repeated in the same order, and (if the 
velocity of rotation be uniform) in equal intervals 
of time. 

Now, in this we have a lively picture of that 
grand phenomenon, the most important, beyond all 
comparison, which nature presents, the daily rising 
and setting of the sun and stars, their progress 
through the vault of the heavens, and their return 
to the same apparent places at the same hours of 
the day and night. The accomplishment of this 
revolution in the regular interval of twenty-four 
hours, is the first instance we encounter of that 
great law of periodicity, which, as we shall see, 
pervades all astronomy ; by which expression we 
understand the continual reproduction of the same 
phenomena, in the same order, at equal intervals of 
time. 

A free rotation of the earth round its centre, if it 
exist and be performed in consonance with the 
same mechanical laws which obtain in the motions 
of masses of matter under our immediate control, 
and within our ordinary experience, must be such 
as to satisfy two essential conditions. It must be 
invariable in its direction with respect to the sphere 
itself, and uniform in its velocity. The rotation 
must be performed round an axis or diameter of the 
sphere, whose poles, or extremities, where it meets 
the surface, correspond always to the same points 
on the sphere. Modes of rotation of a solid body 
under the influence of external agency are con- 
ceivable, in which the poles of the imaginary line 
or axis about which it is at any moment revolving 
shall hold no fixed places on the surface, but shift 
upon it every moment. Such changes, however, 
are inconsistent with the idea of a rotation of a 
body of regular figure about its axis of symmetry, 
performed in free space, and without resistance or 



WONDERS OF THE HEAVENS. 



59 



obstruction from any surrounding medium. The 
complete absence of such obstructions draws with 
it, of necessity, the strict fulfilment of the two con- 
ditions above mentioned. 

Now, these conditions are in perfect accordance 
with what we observe, and what recorded observa- 
tion teaches us in respect of the diurnal motions of 
the heavenly bodies. We have no reason to be- 
lieve, from history, that any sensible change has 
taken place since the earliest ages in the interval of 
time elapsing between two successive returns of the 
same star to the same point of the sky; or, rather, 
it is demonstrable from astronomical records that 
no such change has taken place. And with re- 
spect to the other condition, — the permanence of the 
axis of rotation, — the appearances which any altera- 
tion in that respect must produce, would be marked 
by a corresponding change of a very obvious kind 
in the apparent motions of the stars; Avhich, again, 
history decidedly declares them not to have under- 
gone. 

Such general views of the nocturnal heavens, 
which every c5mmon observer may take, have a 
tendency to expand the mind, and to elevate it to 
the contemplation of an Invisible Power, by which 
such mighty movements are conducted. Whether 
we consider the vast concave, with all its radiant 
orbs, moving in majestic grandeur around our globe, 
or the earth itself whirling round its inhabitants in 
an opposite direction — an idea of sublimity, and of 
Almighty energy, irresistibly forces itself upon the 
mind, which throws completely into the shade the 
mightiest efforts of human power. The most pow- 
erful mechanical engines that were ever construct- 
ed by the agency of man, can scarcely afford us the 
least assistance in forming a conception of that 
incomprehensible Power, which, with unceasing 
energy, communicates motion to revolving worlds. 
And 3^et, such is the apathy with which the hea- 
vens are viewed by the greater part of mankind, 
that there are thousands who have occasionally 
gazed at the stars, for the space of fifty years, who 
are still ignorant of the fact, that they perform an 
apparent diurnal revolution round our globe. 

Again, if we contemplate the heavens with some 



attention, for a number of successive nights, we 
shall find, that by far the greater part of the stars 
never vary their positions with respect to each 
other. If we observe two stars at a certain appa- 
rent distance from each other, either north or south, 
or in any other direction, they will appear at the 
same distance, and in the same relative position to 
each other, the next evening, the next month, and 
the next year. The stars, for instance, which form 
the sword and belt of Orion, present to our eye the 
same figure and relative aspect during the whole 
period they are visible in winter, and from one year 
to another ; and the same is the case with all the 
fixed stars in the firmament. On examining the 
sky a little more minutely, however, we perceive 
certain bodies which regularly shift their positions. 
Sometimes they appear to move towards the east, 
sometimes towards the west, and at other times 
seem to remain in a stationary position. These 
bodies have obtained the name of planets, or wan- 
dering stars ; and, in our latitude, are most fre- 
quently seen either in the eastern and western, or 
in the southern parts of the heavens. Ten of these 
planetary orbs have been discovered; six of which 
are, for the most part, invisible to the naked eye. 
By a careful examination of the motions of these 
bodies, -and their different aspects, astronomers 
have determined that they all move round the sun 
as a centre, and form, with the earth, one grand 
and harmonious system. 

If the results at which we arrive in this age, in 
consequence of the great progress of the physical 
sciences, were unknown to the ancients, still it must 
be admitted that they were not without some idea 
of their existence ; and we are often surprised to 
find a precision, that we should be far from expect- 
ing of them, if we considered sufficiently how much 
patience and reflection were requisite to enable 
them to attain what they have, with the aid of their 
rude methods. However this may be, there was 
nothing better than doubts concerning the motions 
of the heavenly bodies, until the illustrious Coperni- 
cus appeared. He was undoubtedly the first who 
displaced the earth from the centre of the celestial 
motions, and subjected it to the laws, followed by 



3 



60 



WONDERS OF THE HEAVENS 



the other planets, by making it revolve around the 
sun ; and thus destroyed that proud pretension of 
man, that considered the abode he possessed as a 
spot upon which a beneficent Creator had poured 
out all his blessings, and to which he had given, as 
it were, the sovereignty of the universe. 

Some have wished to take from Copernicus the 
immortal glory of such a discovery, by asserting 
that his theory had been already held by certain 
of the ancients. They have mentioned Pythagoras, 
Empedocles, and others. But wise men know how 
to value justly this assertion, and despise the com- 
mon accusation of plagiarism, which so many are 
ever ready to make against those who are guilty 
of having acquired a great reputation. 

The numerous arguments furnished by Coperni- 
cus in support of his theory, caused it to be adopt- 
ed by almost all the astronomers who succeeded 
him ; and those which Kepler, Galileo and New- 
ton added, have served to establish it forever. Let 
us consider now what are the phenomena that 
should result from the rotation of the earth on its 
And first, w^hat induces one ignorant of the 



axis. 



subject to attribute to a motion of the heaven 
what is really a consequence of our own rotation ? 
Experience offers to us daily examples of a similar 
illusion. Placed in a boat that is descending a 
river, if we direct our sight toward the bank, do 
not the hills, the mountains, the trees, all objects 
seem to move in a direction contrary to our own 
motion, and with a rapidity proportioned to their 
proximity to us ? Do not all objects which are 
presented to his vision seem equally to be flying 
backward from the traveller in his coach ? and 
does not the illusion become stronger in proportion 
to the rapidity of his own motion ? 

These effects, and many others similar to them, 
are owing to various causes, the explanation of 
which may be found by examining the sensations 
that affect us in such cases. The motion which 
carries us onward not being the result of the 
voluntary action of our organs, and our relations 
to the objects about us being unchanged thereby, 
we are affected in a manner entirely passive, and 
the cause is not attributed to ourselves. This is 



so true, that, notwithstanding the strong conviction 
we are under that we are subject to a deceitful 
appearance, we cannot at first prevent ourselves 
from believing the erroneous testimony of our 
senses. The circumstances are the same which 
happen to one situated on the surface of the earth. 
All the objects nearest him participate in the same 
motions that are performed so unconsciously by him- 
self, and consequently their motion is unobserved. 
He believes that he and they are motionless, and 
attributes to other objects with which his relations 
are changed a motion in a direction contrary to the 
real motion of himself and those objects that move 
with him. Thus we at first sight should suppose 
that the course of the heavenly bodies was from 
east to west, while in reality it is directly the re- 
verse. The observer, accompanying the earth in 
its rotation, perceives that the heavenly bodies 
become more and more elevated above his horizon, 
and then apparently descend until they are con- 
cealed by the earth, whose opacity prevents the 
passage of luminous rays to the eye of the ob- 
server. 

Before coming to the direct and unanswerable 
proofs of the rotation of the earth, — proofs drawn 
from the laws of attraction and from the many 
phenomena going on about us, — let us reflect a mo- 
ment on the consequences which would result from 
admitting its immobility in space. 

The distance of the sun is about ninety-five mil- 
lions of miles ; consequently, the diameter of the 
circle he would describe around the earth would be 
190 millions, and its circumference 597,142,857, 
which forms the extent of the circuit through which 
he would move in twenty- four hours, if the earth 
were at rest. This number divided by twenty-four 
gives 24,880,952, the number of miles he would 
move in an hour ; and this last number divided by 
sixty gives 414,682, the number of miles he would 
move in a minute. The nearest star is reckoned to 
be at least 20,000,000,000,000, or twenty billions 
of miles distant from the earth ; consequently, its 
daily circuit round our globe would measure more 
than 125,000,000,000,000, miles. This sum divid- 
ed by 86,400, the number of seconds in a day, would 






WONDERS OF THE HEAVENS 



61 



give 1,454,861,111, or somewhat more than one 
thousand fom' hundred millions of miles, for its rate 
of motion in a second of time : a motion which, 
were it actually existing, would, in all probability, 
shatter the universe to atoms. 

The reader may, perhaps, acquire a more dis- 
tinct idea of this explanation from the following 
figure. 




Let the small circle. A, in the centre, represent 
the earth, and the circle B C D E the orbit of the 
sun, on the supposition that he moves round the 
earth every twenty-four hours. The line A B will 
represent the distance of the sun from the earth, 
or ninety-five millions of miles ; the line B D the 
diameter of the orbit he would describe ; and the 
circle B C D E the circumference along which he 
would move every day, or 597 millions of miles, 
which is somewhat more than three times the 
diameter. If the line A F represent the distance 
of the nearest star, the circle F G H I will repre- 
sent the circuit through which it would move 
every twenty-four hours, if the earth were at rest. 
It is obvious, from the figure, that since the stars 
are at a greater distance from the earth than the 
sun, the circle they would describe around the earth 
would be larger in proportion, and, consequently, 
their velocities would be proportionably more 
rapid ; since they would move through their larger 
circles in the same time in which the sun moved 



through his narrower sphere. But the supposition 
that the earth is the centre of all the celestial mo- 
tions, and that the diiferent stars are daily moving 
around it with different velocities, and the slowest 
of these motions is so inconceivably rapid, is so 
wild and extravagant that it appears altogether in- 
consistent with the harmony of the universe, with 
the wisdom and intelligence of the Deity, and with 
all the other arrangements he has made in the 
system of nature. 

How then can we reasonably believe that the 
heavenly bodies, scattered in such numbers through 
the dome of heaven, placed at such different dis- 
tances, so variable in volume and mass, should 
perform their daily revolutions in exactly the same 
time ? And what other probabilities could we not 
bring forward against such a theory, if we would 
seek with care for all that could be found ? 

If it be not proved satisfactorily that the stars 
are at unequal distances from the earth, at least 
this truth is evident with regard to the sun, the 
moon, and the planets. It would be requisite that 
these bodies should have velocities proportioned 
to their respective distances, in order to produce 
the same appearances as would be presented by 
the rotation of the earth. This concert of motion 
seems the more impossible to admit when reflect- 
ing upon the comets ; they move in all directions 
and with all velocities, and yet make this apparent 
revolution about the earth in twenty-four hours ; a 
revolution affected only by the small quantity of 
their own proper motion. And if this unanimity 
of motion, so constant in the midst of so many 
regular variations, present some trifling differences, 
still the equality may be. taken as perfect, and the 
diurnal motion considered as the only instance of 
uniformity in existence. How can we believe that 
the earth, this insensible point of matter, is the 
only one immovable in the midst of bodies so im- 
mense and so rapidly moving ? 

The sentiment of self-love, which would refer 
every thing to ourselves, tempts us to believe our 
earth the centre of the motions of the universe. It 
is the part of philosophy to remove such a cause ; 
or, rather, does not religion remove it ? Is it not 



62 



WONDERS OF THE HEAVENS 



attacking the majesty of the Creator to make the 
creation of all these myriads of bodies have for its 
sole or chief object the lighting up or enlivening of 
this earth, a mere atom in space ? 

When we w^hirl a sling, the hand that holds the 
cord feels that some effori is required to retain it. 
As soon as this effort ceases, the stone, released 
from its confinement, escapes. The power that 
causes the tension of the string is called centrifugal 
force, (tendency from the centre.) Every body, 
thus revolving round a point, has a tendency to 
escape from that centre, in a right line, which is 
tangent to the circle made by the revolving body ; 
while the cord which confines it represents the 
centripetal force (tendency toward the centre) exer- 
cised to retain the body. Calculations show that 
this force increases as the mass of the body and as 
the squares of the velocity of its motion. How im- 
mense then would be the power required to keep 
the sun and the stars in their respective orbits 
round the earth. Thus all things seem to conspire 
to prove to us that the earth has a motion of rotation 
on its axis from west to east, ivhile the stars remain 
fixed. 

Since the earth revolves, it must, like all bodies 
that have a similar motion, possess a centrifugal 
force, which (according to experience and calcula- , 
tion) increases as the squares of the velocities of 
the motion. The equator being the largest circle 
of the earth, the centrifugal force must be greatest 
there. It will, on the contrary, be nothing at the 
poles. And as the centrifugal force varies with 
the distance from the centre of the globe, it follows 
that the force of attraction acts upon bodies on dif- 
ferent parts of the surface with a varying intensity. 

To be convinced of this fact it was only necessa- 
ry to carry a pendulum from the equator toward 
the pole, and as the number of oscillations increase 
with its weight we have a very simple method of 
finding the force of attraction. 

But there are two things to be considered in the 
difference of results with which we should be thus 
furnished ; viz. the greater distance of the body 
fi:'om the centre of attraction, and the greater cen- 
trifugal force at the equator. These two circum- 



stances conspire to make the weight of bodies at 
the equator less than they would be at the poles ; 
weight being an effect of attraction which the earth 
exercises on bodies. It is found that the weight 
decreases as we ascend high mountains, and we 
know that the equatorial diameter is the longest ; 
therefore there is nothing unreasonable in suppos- 
ing that the cause of the diminution of weight is the 
same in both cases, viz., the greater distance from 
the centre. The other conspiring cause of the 
diminution of weight will hardly need an argument, 
viz. the greater rapidity of motion at the equator. 

The attraction of the globe also varies with the 
density of its internal strata, which is unknown. 
It would be scarcely possible to admit that the 
earth were homogeneous, even if observations on 
the length of the pendulum did not contradict the 
idea ; while we find an admirable consistency in 
the theory that the density of the earth increases from 
the surface to the centre. 

A pendulum, then, at the same time that it helps 
to prove the rotation of the earth, introduces us, 
as it were, into the interior of the globe, and per- 
mits us to appreciate the strata which compose it. 
It has been usual to regard the diminution of weight 
at the equator as ^^•, that is, bodies lose at the 
equator ^-^g- of the weight they have at the poles. 
As 289 is the square of seventeen, and as the cen- 
trifugal force increases as the square of the velocity, 
it follows that if the rotation of the earth should 
become seventeen times more rapid than it is, a 
body at the equator would lose the whole of its 
weight. If a still greater velocity were imparted 
to it, bodies would fly off" from the earth's surface, 
as stones rise from the crater of a volcano. 

The reader will naturally inquire what is meant 
by speaking of the same body as having different 
weights at different stations ; and how such a fact, 
if true, can be ascertained. When we weigh a 
body by a balance or a steelyard we do but coun- 
teract its weight by the equal weight of another 
body under the very same circumstances ; and if 
both the body weighed and its counterpoise be re- 
moved to another station, their gravity, if changed 
at all, will be changed equally, so that they will 



WONDERS OF THE HEAVENS. 



63 



still continue to counterbalance each other. A 
difference in the intensity of gravity could, there- 
fore, never be detected by these means ; nor is it 
in this sense that we assert that a body weighing 
194 pounds at the equator will weigh 195 at the 
pole. If counterbalanced in a scale or steelyard 
at the former station, an additional pound placed in 
one or other scale at the latter would inevitably 
sink the beam. 

The meaning of the proposition may be thus ex- 
plained : conceive a weight, x, suspended at the 
equator by a string without weight passing over a 
pulley. A, and conducted (supposing such a thing 
possible) over other pulleys, such as B, round the 
earth's convexity, till the other end hung down at 
the pole, and there sustained the weight y. If, 
then, the weights x and y were such as, at any one 
station, equatorial or polar, would exactly counter- 
poise each other on a ba- 
lance or when suspended 
side by side over a single pul- 
ley, they would not coun- 
terbalance each other in this 
supposed situation, but the 
polar weight, y, would pre- 
ponderate ; and to restore 
the equipoise the weight x 
must be increased by y^jth part of its quantity. 

The means by which this variation of gravity 
may be shown to exist, and its amount measured, 
are twofold, (like all estimations of mechanical 
power,) statical and dynamical. The former con- 
sists in putting the gravity of a weight in equili- 
brium, not with that of another weight, but with a 
natural power of a different kind not liable to be 
affected by local situation. Such a power is the 
elastic force of a spring. Let ABC be a strong 
support of brass, standing on the foot A E D, cast 
in one piece with it, into which is let a smooth 
plate of agate, D, which can be adjusted to perfect 
horizontality by a level. At C let a spiral spring, 
G, be attached, which carries at its lower end a 
weight, F, polished and convex below. The length 
and strength of the spring must be so adjusted 
that the weight F shall be sustained by it just to 





swing clear of contact with the agate plate in the 
highest latitude at which it is intended to use the 
instrument. Then, if small 
weights be added cautious- 
ly, it may be made to de- 
scend till it just grazes the 
agate, a contact which can 
be made with the utmost 
imaginable delicacy. Let 
these weights be noted ; the 
weight F detached ; the 
spring G carefully lifted off 
its hook, and secured, for 
travelling, from rust, strain, 
or disturbance ; and the 
whole apparatus conveyed ililllllliniliilllllillllllllllill 
to a station in a lower latitude. It will then be 
found, on remounting it, that, although loaded with 
the same additional weights as before, the weight 
F will no longer have power enough to stretch the 
spring to the extent required for producing a simi- 
lar contact. More weights will require to be add- 
ed ; and the additional quantity necessary will, it 
is evident, measure the difference of gravity be- 
tween the two stations, as exerted on the whole 
quantity of pendent matter, i. e. the sum of the 
weight of F and half that of the spiral spring itself 
Granting that a spiral spring can be constructed of 
such strength and dimensions that a weight of 
10,000 grains, including its own, shall produce an 
elongation of ten inches without permanently strain- 
ing it, one additional grain will produce a further 
extension of xoVoth of an inch, — a quantity which 
cannot possibly be mistaken in such a contact as 
that in question. Thus we should be provided 
with the means of measuring the power of gravi- 
ty, at any station, to within xoffucjth of its whole 
quantity. 

The other or dynamical process, by which the 
force urging any given weight to the earth may 
be determined, consists in ascertaining the velocity 
imparted by it to the weight when suffered to fall 
freely in a given time, as one second. This ve- 
locity cannot, indeed, be directly measured ; but, 
indirectly, the principles of mechanics furnish an 



Jj 



64 



WONDERS OF THE HEAVENg 



easy and certain means of deducing it, and, con- 
sequently, the intensity of gravity, by observing 
the oscillations of a pendulum. It is proved in 
mechanics that, if one and the same pendulum be 
made to oscillate at different stations, or under the 
influence of different forces, and the numbers of 
oscillations made in the same time in each case be 
counted, the intensities of the forces will be to each 
other inversely as the squares of the numbers of 
oscillations made, and thus their proportion be- 
comes known. For instance, it is found that, 
under the equator, a pendulum of a certain form 
and length makes 86,400 vibrations in a mean solar 
day ; and that when transported to fifty-one and a 
half degrees north, the same pendulum makes 
86,535 vibrations in the same time. Hence we 
conclude, that the intensity of the force urging the 
pendulum downwards at the equator is to that at 
fifty-one and a half degrees north as 86,400 to 
86,535, or as 1 to 1-00315; or, in other words, 
that a mass of matter at the equator weighing 
10,000 pounds exerts the same pressure on the 
gromid, and the same effort to crush a body placed 
below it, that 10,031i of the same pounds, transport- 
ed to fifty-one and a half degrees north, would 
exert there. 

Experiments of this kind have been made, as 
above stated, with the utmost care and minutest 
precaution, to insure exactness in all accessible 
latitudes ; and their general and final result has 
been, to give tb^t for the fraction expressing the 
difference of gravity at the equator and poles. 
Now, it will not fail to be noticed by the reader, 
and will, probably, occur to him as an objection 
against the explanation here given of the fact by 
the earth's rotation, that this differs materially from 
the fraction sl-^, expressing the centrifugal force at 
the equator. The difference by which the former 
fraction exceeds the latter is -j^^j, — a small quantity 
in itself, but still far too large, compared with the 
others in question, not to be distinctly accounted 
for, and not to prove fatal to this explanation, if it 
will not render a strict account of it. 

The mode in which this difference arises affords 
a curious and instructive example of the indirect 



influence which mechanical causes often exercise, 
and of which astronomy furnishes innumerable in- 
stances. The rotation of the earth gives rise to 
the centrifugal force ; the centrifugal force pro- 
duces an ellipticity in the form of the earth itself; 
and this very ellipticity of form modifies its power 
of attraction on bodies placed at its surface, and 
thus gives rise to the difference in question. Here, 
then, we have the same cause exercising at once a 
direct and an indirect influence. The amount of the 
former is easily calculated, that of the latter with 
far more difficulty, by an intricate and profound 
application of geometry, whose steps we cannot 
pretend to trace in a work like the present, and 
can only state its nature and result. 

The weight of a body (considered as undiminish- 
ed by a centrifugal force) is the effect of the earth's 
attraction on it. The attraction of the earth, then, 
on a body placed on its surface, is not a simple 
but a complex force, resulting from the separate 
attractions of all its parts. Now, it is evident, that 
if the earth were a perfect sphere, the attraction 
exerted by it on a body anywhere placed on its 
surface, whether at its equator or pole, must be 
exactly alike, for the simple reason of the exact 
symmetry of the sphere in every direction. It is 
not less evident that, the earth being elliptical, 
and this symmetry or similitude of all its parts not 
existing, the same result cannot be expected. A 
body placed at the equator, and a similar one at 
the pole of a flattened ellipsoid, stand in a different 
geometrical relation to the mass as a whole. This 
difference, without entering further into particulars, 
may be expected to draw with it a difference in its 
forces of attraction on the two bodies. Calculation 
confirms this idea. It is a question of purely 
mathematical investigation, and has been treated 
with perfect clearness and precision by Newton, 
Maclaurin, Clairaut, and many other eminent geo- 
meters ; and the result of their investigations is to 
show that, owing to the elliptic form of the earth 
alone, and independent of the centrifugal force, its 
attraction ought to increase the weight of a body 
in going from the equator to the pole by almost 
exactly -s^trth part ; which, together with j|^th 



WONDERS OF THE HEAVENS 



65 



due to the centrifugal force, make up the whole 
quantity, ri^th, observed. 

We shall next proceed to state some of the re- 
markable effects resulting from the diurnal rota- 
tion of the earth. 

When we abandon a body to the action of gravi- 
ty it falls ; its direction would be vertical if the 
earth were at rest. And if the point whence we 
let it fall be not far from the surface of the earth, 
the direction of its descent would not be apprecia- 
bly out of the vertical, on the supposition that the 
earth revolves. But let a body be carried to a 
very high summit, is it not evident that it would 
acquire a velocity of rotation proportioned to the 
height of the summit, that is, to its distance from 
the axis of motion ? It will therefore acquire a 
velocity in a horizontal direction greater than the 
base of the edifice or mountain. But this swiftness 
of motion from the west towards the east, that is, 
in the direction of the earth's rotation, it retains 
when left to itself, and acquires another from 
gravity, in the direction of the vertical. Being 
thus, acted upon by two forces, it would fall in the 
resultant of the two, and strike the ground a little 
to the east of the tower. This experiment is a 
very delicate one, for a fall of two hundred feet 
causes but very slight deviation from the vertical ; 
yet it has often been tried, and has always agreed 
with the theory. Although such an experiment 
would be unsatisfactory by itself, because of the 
small scale on which it can be tried, it may make 
one link in the great chain of evidence that so irre- 
sistibly proves the rotation of the earth on its axis. 

Another effect of the revolution of the earth is 
the displacement of the air in the equatorial regions. 
The air, heated by the action of the sun, expands, 
and, rising, passes toward the poles, while the 
denser air at the poles rushes, in different direc- 
tions, to fill up the void under the equator. In their 
contact with the earth the particles acquire the 
same velocity of rotation as the zone they occupy. 
When, therefore, they reach the equator, they 
would receive an increase of rapidity if they could 
remain long enough in contact with that part of the 
globe ; but as the air is constantly expanding and 



rising there, it never acquires a velocity equal to 
that of the equator. Wherefore the trees, houses, 
mountains, ships, turning with the rapidity of the 
earth, strike with force upon the air, producing the 
same effect and appearance as if they were still and 
the air in motion. 

The following on this subject is from " Arnott's 
Physics." 

If our globe were at rest, and the sun were al- 
ways acting over the same part, the earth and air 
directly under him would become exceedingly heat- 
ed, and the air would be constantly rising, like oil 
in water, or like the smoke from a great fire; 
while currents or winds below would be pouring 
towards the central spot from all directions. But 
the earth is constantly turning round under the sun, 
so that the whole middle region or equatorial belt 
may be called the sun's place; and therefore, ac- 
cording to the principle just laid down, there 
should be over it a constant rising of air, and con- 
stant currents from the two sides of it, on the north 
and south, to supply the ascent. Now this phe- 
nomenon is really going on, and has been going on 
ever since the beginning of the world, producing 
the steady winds of the northern and southern 
hemispheres, called the trade winds, on which, in 
most places within thirty degrees of the equator, 
mariners reckon almost as confidently as on the 
rising and setting of the sun himself. 

The trade winds, however, although thus moving 
from the poles to the equator, do not appear on the 
earth to be directly north and south, for the east- 
ward whirling, or diurnal rotation of the earth, 
causes a wind from the north to appear as if coming 
from the north-east, and a wind from the south as 
if coming from the south-east. 

This fact is illustrated by the case of a man on a 
galloping horse, to whom a calm appears to be a 
strong wand in his face ; and if he be riding east- 
ward while the wind is directly north or south, 
such wind will appear to him to come from the 
north-east or south-east ; or, again, by the case of 
a small globe made to turn upon a perpendicular 
axis, while a ball or some water is allowed to run 
from the top of it downwards ; the ball will not 



66 



WONDERS OF THE HEAVENS 



immediately acquire the whirling motion of the 
globe, but will fall almost directly downwards ; but 
the track, if marked upon the globe, will appear 
not as a direct line from the axis to the equator, 
that is, from north to south, but as a line falling 
obliquely. Thus, then, the whirling of the earth 
is the cause of the oblique and westward direction 
of the trade winds, and not, as has often been said, 
the sun drawing them after him. 

The reason why the trade winds, at their exter- 
nal confines, which are about thirty degrees from 
the sun's place, appear almost directly east, and 
become more nearly north and south as they ap- 
proach the central line, is, that at the confines they 
are like fluid coming from the' axis of a turning 
wheel, and which has approached the circumfer- 
ence, but has not yet acquired the velocity of the 
circumference; while, nearer the line, they are 
like the fluid after it has for a considerable time 
been turning on the circumference, and has acquired 
its rotary motion; consequently appearing at rest 
as regards that motion, but still leaving sensible any 
motion in a cross direction. 

While, in the lower regions of the atmosphere, 
air is thus constantly flowing towards the equator 
and forming the steady trade winds between the 
tropics, in the upper regions there must of course be 
a counter current, distributing the heated air over 
the globe. Accordingly, since reason led men to ex- 
pect this, many striking proofs have been detected. 
At the summit of the Peak of Teneriffe, observa- 
tions now show that there is always a strong wind 
blowing in a direction contrary to that of the trade 
wind on the face of the ocean below. Again, the 
trade winds among the West India islands are con- 
stant, yet volcanic dust thrown aloft from the island 
of St. Vincent, in the year 1812, was found, to the 
astonishment of the inhabitants of Barbadoes, 
hovering over them in thick clouds, and falling, 
after coming more than one hundred miles directly 
against the strong trade wind, which ships must 
take a circuitous course to avoid. To persons sail- 
ing from the Cape of Good Hope to St. Helena the 
sun is often hidden for days together, by a stratum 
of dense clouds passing southward high in the at- 



mosphere; which clouds consist of the moisture 
raised high near the equator with the heated air, 
and becoming condensed again as it approaches the 
colder regions of the south. 

Beyond the tropics, where the heating influence 
of the sun is less, the winds occasionally obey other 
causes than those we have now been considering, 
which causes have not yet been fully investigated. 
The winds of temperate climates are in consequence 
much less regular, and are called variable; but still, 
as a general rule, wherever air is moving towards 
the equator from the north or south poles, where it 
was at rest, it must have the appearance of an east 
wind, or a wind moving in a contrary direction to 
the earth itself, until it has gradually acquired the 
whirling motion of that part of the surface of the 
earth on which it is found; and again, when air is 
moving from the equator, where it had at last ac- 
quired nearly the same motion as that part of the 
earth, on reaching nearer the poles, and which 
have less eastward motion, it continues to run 
faster than they, and becomes a westerly wind. In 
many situations beyond the tropics, the westerly 
winds, which are merely the upper equatorial cur- 
rent of air falling down, are almost as regular as 
the easterly winds within the tropics, and might also 
be called trade winds. Witness the usual shortness 
of the voyage from New York to Liverpool, and the 
length of those made in the contrary direction. 
North of the equator, then, on the earth, true north 
winds appear to be north-east, and true south 
Avinds appear to be south-west, which are the two 
winds that blow in England for three hundred days 
of every year. In southern climates the converse 
is true. 

Among the many proofs of the wisdom and good- 
ness of the Deity, one is drawn from the rotation 
of the earth, or rather from the situation of its axis 
of rotation. Among the possibilities out of which 
the choice was to be made, the number of those 
which were wrong bore an infinite proportion to 
the number of those which were right. We have 
already shown that the earth is an oblate spheroid, 
shaped something like an orange. Now the diame- 
ters upon which such a body may be made to turn' 



WONDERS OF THE HEAVENS 



67 



round, or the axes of rotations, are as many as can 
be drawn through its centre to opposite points upon 
its whole surface ; but of these axes none are per- 
manent except either its shortest diameter, i. e. 
that which passes through the heart of the orange 
from the place where the stalk is inserted, and 
which is but one; or its longest diameters, (at right 
angles with the former,) which must all terminate 
in that circumference that goes round the thickest 
part of the fruit. The shortest diameter is that 
upon which the earth in fact turns, and it is, as the 
reader sees, what it ought to be, a permanent axis. 
Whereas, had blind chance, had a casual impulse, 
had a stroke or push at random, set the earth re- 
volving, the odds were infinite but that they had 
sent it round on a wrong axis. And what would 
have been the consequence? When a spheroid, in 
a state of rotation, gets upon a permanent axis, it 
keeps there; it remains steady and faithful to its 
position; its poles preserve their direction with 
respect to the plane and to the centre of its orbit. 
But whilst it turns upon an axis which is not per- 
manent, (and the number of these infinitely exceeds 
the number of the others,) it is always liable to 
shift and vacillate from one axis to another, with a 
corresponding change in the inclination of its poles. 
If therefore a planet once set off revolving upon 
any other than its shortest or one of its longest 
axes, the poles on its surface would be perpetually 
changing, and it would never attain a permanent 
axis of rotation. The effect of this instability would 
be, that the equatorial parts of the earth might be- 
come the polar, or the polar the equatorial, to the 
utter destruction of plants and animals, which are 
not capable of interchanging their situation, but are 
respectively adapted to their own. As to our- 
selves, instead of rejoicing in our temperate climate, 
and annually preparing for the moderate vicissitude, 
or rather the agreeable succession of seasons Avhich 
we experience and expect, we might be suddenly 
locked up in the ice and darkness of the Arctic 
circle, with bodies neither inured to its rigors, nor 
provided with shelter or defence against them. 
Nor would it be much better if the trepidation of 
our pole, taking an opposite course, should place 



us under the heats of a vertical sun. But if it 
would fare so ill with the human inhabitant, who 
can live under greater varieties of latitude than any 
other animal, still more noxious would it prove to 
the rest of creation, the beasts and the plants. 
The habitable earth, with its beautiful variety, 
might have been destroyed by a simple mischance 
in the axis of rotation. 

By virtue of the simplest law that can be 
imagined, viz. that a body continues in the state in 
which it is, whether of motion or rest; and if in 
motion that it goes on in the same line in which it 
was proceeding, and with the same velocity, unless 
there be some cause for change, it comes to pass 
that cases arise in which attraction, incessantly 
drawing a body toward a centre, never brings, nor 
ever will bring the body to that centre, but keep it 
in eternal circulation round it. If it were possible 
to fire off a cannon ball with the velocity of five 
miles a second, and the resistance of the air could 
be taken away, the ball would forever wheel round 
the earth, instead of falling upon it. 

Attraction varies reciprocally as the square of 
the distance ; that is, at double the distance it has 
a quarter of the force; at half the distance four 
times the force ; and so on. Concerning this law of 
variation three things are to be observed : 

I. That attraction, for any thing we know to the 
contrary, was originally indifferent to all laws of 
variation, or just as susceptible of one law as an- 
other. It might have been the same at all dis- 
tances; it might have increased as the distance 
increased ; it might have diminished with the in- 
crease of the distance; yet, amid ten thousand 
different proportions, it might have followed no 
stated law. If attraction be a primordial property 
of matter, then, by the very nature and definition 
of a primordial property, it stood indifferent to all 
laws. If it be the agency of something immaterial, 
then also, for any thing we know, it was indiffer- 
ent to all laws. If the revolution of bodies round a 
centre depend upon vortices, neither are these 
limited to one law more than another. Attraction 
is sometimes ascribed to an emanation from the 
attracting body. But how is it possible that parti- 



68 



WONDERS OF THE HEAVENS 



cles streaming from a centre should draw a body 
toward that centre ? The impulse is all the other 
way. If we imagine particles incessantly flowing to 
the centre we are no better off; for by what source 
is the stream fed, or what becomes of the accumu- 
lation? There is nothing to support the theory of 
emanations excepting the one solitary circumstance, 
that the variation of the attracting force agrees with 
the variations of the density of the rays. 

n. Out of an infinite number of possible laws, 
those which were admissible, i. e. consistent with 
the preservation of the system, lay within narrow 
limits. If the attracting force had varied according 
to any direct law of the distance, great destruction 
and confusion would have taken place. The direct 
simple proportion of the distance would have pro- 
duced an ellipse, but then the perturbing forces 
would have so acted as to be continually changing 
the dimensions of this ellipse, in a manner inconsis- 
tent with our terrestrial creation. Of the inverse 
laws, if the centripetal force had varied with the 
cube of the distance, or in any higher proportion, 
i. e. if at double the distance the attractive force 
had diminished to an eighth part, or to less than 
that, the consequence would have been, that if the 
earth once began to approach the sun, it would fall 
into his body, or if it once, though ever so little, in- 
creased its distance from the centre, it would recede 
from it forever. The laws of attraction therefore, 
consistent with the safety of the universe, lie within 
narrow limits, compared with the possible laws. 

We do not know, or rather we seldom reflect, 
how interested we are in this matter. Small irregu- 
larities may be endured, but (small changes except- 
ed) the permanence of the ellipse is a question of 
life and death to the whole sensitive world. 

III. Of the different laws that may be considered 
among the admissible, we say that the best has been 
chosen ; that there are advantages in this particular 
law which do not belong to any of the rest. 

While this law prevails between each particle of 
matter, the ujiited attraction of a sphere, composed 
of matter, observes the same law. This property 
of the law is necessary to render it applicable to a 
system composed of spheres ; yet it belongs to no 



other admissible law of attraction. If we go further, 
we shall more strikingly perceive that this regula- 
tion proceeded from a designing mind. A law 
both adinissible and convenient was requisite. In 
what way is the law of the attracting globes attain- 
ed ? Observations and experiments show, that the 
attraction of the globes of the system is made up of 
the attraction of their parts. Here then are clear- 
ly shown regulation and design. A law admissible 
and convenient was to be obtained; the mode 
chosen for obtaining it was by making each particle 
of matter act. After this choice was made, one 
and one only particular law of action was to be 
assigned, and no other law but the one they have 
received would have answered the intended pur- 
pose. 

All systems must be liable to perturbations. To 
guard against their running to destructive lengths, 
is perhaps the strongest evidence of care and fore- 
sight that can be given. It can be demonstrated 
of our law of attraction, and can be of no other, 
that the action of the parts of our system upon one 
another will not cause permanently increasing 
irregularities, but merely periodical or vibratory 
ones; that is, they will come to a limit and then 
go back again. To make this hold, several cir- 
cumstances are necessary ; viz. : the force must be 
inversely as the square of the distance ; the masses 
of the revolving bodies must be small, compared 
with that of the body at the centre ; the orbits not 
much inclined to each other, and their eccentricity 
small. In such a system the important points are 
secure. The mean distances and periodic times 
are constant; the eccentricities vary so slowly and 
to so small an extent as to produce no incon- 
venience. The same is true of the obliquity of the 
planes of the orbits. The inclination of the ecliptic 
to the equator will not change above two degrees, 
and that change requires many thousand years. 

If it be said that the planets might have been 
sent round the sun in exact circles, in which case, 
no change of distance from the centre taking place, 
the law of variation of the attracting power would 
never have come in question, one law would have 
served as well as another ; an answer to the scheme 



WONDERS OF THE HEAVENS 



69 



may be drawn from the consideration of these same 
perturbing forces. The system retaining in other 
respects its present constitution, though the planets 
had been sent round in exact circles, they could 
not have kept them: and if the law of attraction 
had not been what it is, or, at least, if the prevail- 
ing law had transgressed the limits above assigned, 
every movement would have been productive of 
fatal consequences. The planet once drawn (as it 
necessarily must have been) out of its course, would 
have wandered in endless error. 



SECTION II. 

Sun's apparent motion — Ecliptic — Celestial latitude and longitude — 
Tropics — Does the sun really move in the ecliptic? — Impulse 
requisite to produce the motions of the earth — Appearance of the 
motions of the planets as seen from the sun — System of Tycho 
Brahe — Proofs of the earth's double motion — Annual parallax — 
Axis of the earth always points to the same celestial poles — Its 
inclination to the ecliptic — Radius vector — Cause of the change 
of seasons — Zones — Winter at the poles — Illustration of the fore- 
going — Nature of the earth's orbit — Poetical rising and setting of 
the stars — Perihelion and aphelion — Designing wisdom apparent 
from the figure of the earth's orbit. 

Beside the daily motion that has been mentioned, 
the earth has also another, which carries it in an 
elliptical orbit about the sun, the centre of our 
planetary system. In order to arrive at the know- 
ledge of this motion, we shall examine the appear- 
ances that are presented to our senses. 

At all times people have been struck with the 
alternate departure and approach of the sun, and 
with the variations of his height according to the 
seasons. If, in fact, we observe each day the right 
ascension and declination of this body, we shall find, 
that they are never twice the same ; if we compare 
the sun's path with that of any star whatever, we 
shall find, that in relation to the star it advances 
daily about one degree towards the east. But one 
degree answers to four minutes of time. It arrives 
then four minutes later in the plane of the meridian 
than the star. These four minutes accumulating, 
it results, that after ninety days the distance to the 
same star will be about ninety degrees, or six hours. 



After one hundred and eighty days the star and the 
sun will be in the plane of the meridian at the same 
time ; but the latter will pass the lower meridian 
while the first will be on the upper meridian. 
Finally, after three hundred and sixty-five days 
and a quarter, that is to say, one year, the two 
bodies will be found at the same time in the plane 
of the same meridian-, the star having passed by 
this plane once more than the sun. And the same 
relative changes will be renewed the following year. 
If we have taken care to trace each day on a-sphere 
the different points at which the sun is found at the 
same hour of the day, we shall thus have a curve 
which will be the track of its apparent motions 
during a whole year. 

Observation has taught us that the plane of this 
curve, which has been called the ecliptic, (because 
the moon is always in or near it when she is 
eclipsed,) passes through the centre of the earth: 
its direction is oblique to the equator, and the an- 
gle that it makes with this great circle is equal to 
23° 28'. This angle constitutes the obliquity of 
the ecliptic. It has for its complement the distance 
from the most northerly or southerly point of this 
curve to the pole, which is 66° 32'. The great 
circle of the celestial sphere, that corresponds to 
the track of the ecliptic on the earth, has received 
also the same name. The position of the stars, or 
of the different points of the heavens, are referred 
either to the horizon and the meridian, which are 
fixed for each terrestrial place, or to the celestial 
equator and a particular horary circle. The dis- 
tance of any point from these last curves is called 
its declination and right ascension. A third method 
exists, which is of continual use in astronomy. A 
great part of the phenomena of the planetary 
system takes place near the plane of the ecliptic; 
it was therefore necessary to refer the heavenly 
bodies to this plane. For this purpose, we imagine, 
at each point of the heavens, a great circle perpen- 
dicular to the plane of the ecliptic. This is called 
a circle of latitude. Then the position of a star is 
determined by two elements : the first is the arc of 
a great circle, contained between the ecliptic and 
the star. This arc is called the latitude of the star. 



J 



70 



WONDERS OF THE HEAVENS 



The second is the arc of the ecliptic, contained 
between the vernal equinox and the circle of lati- 
tude. This arc is computed, like the right ascen- 
sion, from west to east, in the direction of the sun's 
apparent motion, and is called the longitude of the 
star. The longitude and latitude of stars are not 
taken by immediate observation, but are deduced 
by trigonometrical calculations from their right 
ascension and declination. 

The different positions of the sun in the ecliptic 
account for the variety of the seasons and the 
change in the length of the days. When it is in 
the plane of the equator, it apparently describes 
that circle in twenty-four hours ; but as it departs 
from this plane, and advances (for example) in the 
northern hemisphere, it describes a series of paral- 
lels, which diminish each day, until it has reached 
its greatest distance from the equator, which is, as 
we have said above, 23° 28'. The parallel which 
it. here describes has received the name of tropic, 
from a Greek word, which means return, because, 
when once this revolution is accomplished, it begins 
to return, again advancing toward the equator; 
and having passed it, approaches the most souther- 
ly point of the ecliptic in the opposite hemisphere, 
and returns again toward the equator ; thus repro- 
ducing each year the phenomena of the preceding. 
It is evident that, on account of the continual mo- 
tion of the sun in the ecliptic, the parallels that it 
describes each day will not be true circles, but 
spirals, such as we form when winding a ball of 
thread. 

Let E E' be the equator, G and G' the most 
elevated points of the. ecliptic, to which we give 
the name of solstices, because the sun seems to stop 
at these places ; the parallels G g' and g G' will be 
the circles called tropics. When the sun is at one 
of the solstices, the countries which are near this 
point will have summer; those will have winter 
that are the most distant from this point. As to 
the days, the longest will be when the sun is in the 
summer solstice; the shortest, when the sun is at 
the winter solstice. 

The time of the equinoxes, during which the 
days and nights are equal, happens always when 



the sun is in the plane of the equator. This is the 
case twice in each year; and for us it is spring 




when the sun comes toward the northern hemis- 
phere, and autumn when it passes again into the 
southern hemisphere. 

Such are the different appearances which the sun 
successively presents to us in its orbit, returning to 
the point whence it set out. The time required 
for its apparent revolution is called a year. But 
ought we to attribute to the sun himself the motions 
that we have noticed ? We are already convinced 
that we must not always trust the evidence of our 
senses; and besides, if we reason according to the 
principles we have employed on the subject of the 
revolution of the earth about its axis, we shall soon 
be persuaded that it will be hazarding a supposition 
but little probable to regard a§. real an apparent 
motion. It would, in fact, be necessary to suppose 
the velocity of the sun so tremendous, that it is 
much more simple to think that the earth itself goes 
over the orbit of which w^e have above spoken. 
Calculation gives for the earth's motion eleven 
hundred and thirty-three miles as the space de- 
scribed in one minute, which is eighteen miles and 
three quarters a second. This swiftness of motion 
ought not to surprise us ; for the more careful ob- 
servation of the phenomena which the planets 
present will furnish us with similar movements; 
we shall see that, like our globe in form, they are 
also, like it, possessed of a double motion, one of 
translation in space, the other of rotation on their 
axes. 

By the laws of mechanics, in order that a free 



WONDERS OF THE HEAVENS. 



71 



body may be struck so as to turn on its axis, it is 
necessary that the impulse should not pass through 
the centre of gravity. Beside its revolution, it 
takes also a motion of translation, as if the force 
had acted on its centre, so that it is carried through 
space, while turning on its axis. If the force which 
moves a ball on the billiard table is not in the 
direction of the centre of this ball, it will revolve 
at the same time that it advances in the direction 
of the blow. In order that the rotation should 
exist alone, a second impulse, equal and opposite, 
must be impressed at the same time on the centre, 
capable of arresting its onward motion. We are 
assured that the earth has a motion of revolution in 
twenty-four hours ; and that whatever be the cause 
of it, the globe could not have received this motion 
without another motion, viz. that of its centre being 
transported in space, unless an opposite force had 
prevented it. It is therefore more simple to sup- 
pose the earth possessed of this second motion, than 
to attribute it to the sun. In fact, there must be 
three impulses to produce the phenomena on the 
last supposition : one on the centre of the sun ; the 
second on the earth, to make it turn on its axis; 
the third, equal and opposite to this, to arrest and 
fix it in space. We shall not speak here of the 
causes which make one of these bodies revolve 
about the other, or of the force which retains it in 
its orbit; these things being foreign to the part of 
the subject on which we are now occupied. 

There are intermediate bodies between us and 
the stars, and which have, like the earth, a motion 
of their own. In observing these (which are called 
planets) with good telescopes, spots have been 
seen on their surfaces, the motion of which proves 
a revolution of these bodies on their axis, precisely 
similar to the rotation of the earth. All these 
bodies are opaque, like our globe, and are a little 
flattened at the poles, revolving about the sun, 
each in its own orbit, from west to east, like the 
earth. Some of them have their moons, as we have 
ours. A spectator placed on the sun, if the vivid 
light of that body did not deprive him of the view 
of the celestial bodies, would see the planets re- 
volving about him, while turning on their own 



axes ; the earth being subjected to the same general 
law as the rest. 

The more distant the planets are from the sun, 
the slower is their motion around it : nor is the 
earth, any more than the other bodies of the system, 
free from the action of this general law. The 
analogy is complete. All things conspire to warrant 
us in classing this globe in the number of the pla- 
nets. If we will believe that the sun has an annual 
motion in the ecliptic, we destroy the simplicity of 
this admirable system. Beside, it will be necessary 
to admit the revolution of the planets around the 
sun ; the sun will thus carry off their orbits with 
it in space, compelling them to follow in its march 
about us : — a system very complicated. Yet such 
was the system of Tycho Brahe. 

The rapidity of the earth's motion should not 
create any surprise, since that of Venus is much 
greater ; for she describes twelve hundred miles in 
a minute. The size of this planet is nearly equal 
to that of the earth. And what a prodigious force 
must that be which moves Jupiter and Saturn, 
which are, one fifteen hundred, and the other nine 
hundred times greater than our globe ! Why 
cannot the earth be moved like these bodies ? An 
observer placed on Jupiter would suppose the sun, 
the earth, and the planets in motion about him: 
and the great size of his globe would render this 
illusion more probable to him than to us. 

The annual motion of the earth or that of the 
sun are the two hypotheses between which we 
must choose. The first of these suppositions is the 
most simple, since it ascribes motion only to a 
point scarcely visible to a spectator placed on the 
sun; while we are obliged to acknowledge that 
other celestial bodies, of greater volume than our 
earth, are subjected to the same motion. Is it not 
natural to prefer a system which bears the character 
of truth, and respects the conditions of analogy, 
which we destroy by a contrary opinion ? 

And as to the two motions of the earth, its 
diurnal rotation on its axis and its annual motion 
in the ecliptic; far from regarding this double 
action as complicated, we should recollect that, 
besides the fact of their existing in the planets. 



72 



WONDERS OF THE HEAVENS 



where they oflfer nothing surprising, the motion in 
its orbit is a consequence, according to the princi- 
ples of mechanics, of that force which causes the 
rotary motion. If the last existed alone, there 
must be more power to produce it, more effort of 
the mind to conceive it. 

It is thus the toy we call a top, by a lateral 
impulse, turns rapidly on its axis, while its point 
describes a curve on the plane of the horizon. In 
other respects this comparison is very imperfect, 
since the air, the friction, the manner in which the 
top is thrown, tend to destroy its motion of trans- 
ference in the beginning. That of the earth, which 
no resistance diminishes, seems, on the contrary, 
to be constant and unchangeable. 

Let us admit therefore the theory of the double 
motion of the earth, and, far from considering it as 
lightly adopted, let us rather admire the great 
number of proofs it unites. In fact, this motion 
might not have been confirmed by the motion of 
the planets; for these bodies might not have 
existed at all, or they might not have had both 
their motions from west to east, or they might have 
been without moons, or, finally, they might have 
been smaller than the earth, and less distant from 
the sun. Yet there would still be, in the appear- 
ances of the sun alone, proofs enough to make us 
prefer the hypothesis of the motion of the earth to 
that of the sun. 

But what gives the greatest weight to this 
opinion is the admirable agreement it establishes 
between observations and results. The most 
minute details, and the most delicate calculations, 
have not discovered any thing in their consequences 
inconsistent with the phenomena; any thing not 
agreeing rigorously with prediction. The proofs 
drawn from attraction and aberration cannot now 
be exhibited : and these are the only mathematical 
ones. Whatever is contained in the following part 
of this treatise, is, properly speaking, only a series 
of proofs of the double motion of the earth. This, 
which was at first only a supposition, (though 
infinitely more probable than the contrary opinion,) 
will become a truth demonstrated by more proofs 
than any theorem in physics, whether we consider 



the simplicity of the laws which result from it, or 
the analogy which it establishes in all parts of the 
system. 

According to this, the centre of the earth will 
therefore describe about the sun, immovable in 
space, a continuous curve line in three hundred 
and sixty-five days and a quarter, from west to 
east, while, at the same time, it makes each day a 
revolution on its axis, in the same direction. Its 
axis remains parallel with itself in all its positions, 
forming with the plane of its orbit, which is the 
ecliptic, an angle of 66° 32'. A spectator, sepa- 
rated from the earth, who should follow it in the 
ecliptic, with his face turned toward the north pole, 
would have the sun constantly on his left, and 
would see our globe move in the course already 
mentioned, and at the same time turning on its 
axis, the disc visible to him passing from his left 
to his right. 

A little after sunset, when the twilight begins to 
diminish, we perceive half of the celestial sphere. 
The heavens seem to us to turn slowly from east 
to west. The stars disappear on one side of the 
horizon, and on the opposite side others rise. 
This apparent revolution continues during the 
night, and the extent of the firmament which is 
successively exhibited to our view depends on the 
duration of the darkness. In one night in winter 
or autumn we m,ay see, in this latitude, almost the 
wdiole heavens, except the part near the south 
pole, which never rises to us, and that which is 
near the point of the ecliptic where the sun appears, 
this last portion, rolling over our heads wdth the 
star of day, is concealed from us by its superior 
light. Such are the appearances produced by the 
rotation of the earth on its axis in twenty-four 
hours. 

The sun seems to us to pass over the ecliptic in 
the same direction that the earth in reality de- 
scribes this curve. If the earth is in the sign of 
the Ram, the sun will seem to us to occupy the 
opposite point, in the sign of the Balance; if the 
earth moves to the sign of the Bull, the sun will 
appear to us in the sign of the Scorpion; if the earth 
is in the Tivins, we shall suppose the sun in the 



WONDERS OF THE HEAVENS 



73 



Archer. Thus, while the earth passes over one 
half of the boundary line of the ellipse, the sun 
appears to be describing the other half and in the 
same direction, viz. frora west to east. 

The largest base which at first could be used for 
a scale to measure considerable distances, was the 
diameter of the earth, which is nearly eight thou- 
sand miles. But when we have obtained with 
precision the solar parallax, and from it have 
determined the diameter of the ecliptic, we may 
take this for our base. It is by this means that we 
find with precision the distance of the planets from 
the sun. The motion of the earth, which, by the 
illusions it causes, for a long time retarded the 
knowledge of the real motions of the planets, 
makes them known to us with more precision than 
if we were fixed in the centre. 

Since the axis of the earth continues parallel to 
itself, and makes with the plane of its orbit an 
angle of 66° 32', we should suppose that the 
extremities of the axis must mark out, on the hea- 
vens and about the poles, two continuous curves, 
of an extent proportioned to that of the ecliptic, 
and to the radius of the celestial sphere. This is 
not so ; but the axis, if prolonged, would reach two 
points invariably opposite. This results from the 
infinite distance of the stars. We have said that 
the dimensions of the earth are nothing compared 
to this distance. The same may be said of the 
diameter of the ecliptic itself, although this diame- 
ter is nearly two hundred millions of miles. Let 
us note with care the distance of a star on the 
ecliptic; after six months, the earth having passed 
over half of its orbit, if the annual parallax exists, 
this distance will vary gradually, in this time, the 
whole amount of that angle. But astronomers have 
never been able to observe the least change ; and 
as they can measure with exactness an arc of two 
seconds, we must conclude that if the annual 
parallax were equal to two seconds it would have 
been discerned. 

Some astronomers have thought they observed 

this parallax of two seconds in Sirius and Vega of 

the Harp. These, then, which, by reason of their 

brilliant light, seem to be the nearest of the stars, 
10 



must be at least one hundred thousand times more 
distant than the sun. The diameter of the ecliptic 
is too small a base to enable us to measure the 
distance of the stars. The earth, having gone over 
three hundred millions of miles, must advance about 
one hundred thousand times farther in space to 
arrive at Sirius, which is more than 20,000,000,- 
000,000 of miles distant from us ; and perhaps 
must pass over another equal space to reach the 
stars of the second magnitude. What immensity ! 
A spectator placed in Sirius will see the sun only 
under an angle of a hundredth part of a second at 
most, the orbit of the earth under an angle of 
scarcely four seconds, and the thickness of a thread 
of silk will be sufficient to hide the whole planetary 
system. 

Thus the axis of the earth always points to the 
same celestial poles ; for parallels meet when 
infinitely produced. The plane of the equator, 
carried onward with the annual motion, preserves 
a constant parallelism with itself, whilst it forms 
with the ecliptic an angle of twenty-three and 
a half degrees, and marks out in the heavens a 
circle bearing the same name, (celestial equator,) 
in the same manner as if the earth were without 
its motion of revolution. The movements of the 
earth in no way contradict the observation respect- 
ing the fixed place of the poles and of the celestial 
equator. 

Let us now imagine ourselves transported to the 
sun, (its body being supposed transparent,) and let 




us thence direct our sight to the earth ; we shall 
perceive that it is endowed with a rotation on its 
axis in twenty-four hours ; and with another motion, 



74 



WONDERS OF THE HEAVENS. 



in which its centre describes a curved line in three 
hundred sixty-five and one fourth days nearly ; the 
axis remaining parallel to itself all the while. 

The line S E, that joins the centres of the 
sun and earth, is called the radius vector. This 
ideal line the earth carries with it through space, 
its length always varying with the earth's distance 
from the sun. 

If we fasten a body to the end of an elastic cord, 
and whirl it around in such a way that its rapidity 
in various points of the curve would be different, 
the lengths would vary with the velocity of the mo- 
tion, and would exactly represent what is called, 
in regard to the earth's annual motion, the radius 
vector. The orbit, which is also called the 
ecliptic, we shall see hereafter is not a circle ; and 
while the diurnal rotation is uniform, the rapidity 
of the motion in the ecliptic is not so. 

We shall, however, first show, that the change 
of seasons is owing to the maintenance of the same 
angle of inclination between the axis of the earth 



jCatjiam 



u/znti 




djarina 

and its orbit at every point of that curve. Let T 
be our globe; the radius vector meets the surface 
at A. The plane A B, perpendicular to the axis 
P T, marks out the circle A B, each point of 
which comes in turn to A by reason of the diurnal 
rotation. The sun being supposed fixed at S, the 
inhabitants of the different points of the circle A B 
will in turn have the sun in their zenith: there will 
be no shadows at midday, and the image of the 
sun will be reflected from the bottom of the wells. 



If T is the equator, A designates the latitude 
of the places on the circle A B. 

Suppose then the earth were at T, a position in 
which the projection of the axis P T on the plane 
of the orbit would coincide with the radius vector 
S T, or the plane P T A would be perpendicular 
to the plane of the ecliptic. The time when the 
earth is in this point is the summer solstice. The 
inhabitants of the zone A P B will not have the 
sun in their zenith, but this is the time when it 
rises nearest to that point. The circle B A will 
be the most northerly circle among those that the 
sun appears to describe in twenty-four hours, being 
distant from the equator twenty-three and a half 
degrees, and named the tropic of Cancer. When 
the earth has left this point and arrived at T', 
diametrically opposite, the axis P' T' being parallel 
to P T, and its projection again falling on the 
radius vector, the inhabitants of that part of the 
earth that had midsummer in the situation first 
mentioned will now have miclivinier. 

At midday the sun is in the zenith to the inhabi- 
tants of the circle A' B', which is twenty-three and 
a half degrees south pf the equator, and is named 
the tropic of Capricorn. The circle in the heavens 
directly over it has the same name, and is the most 
southerly of those circles that the sun appears to 
describe in twenty-four hours. 

Let us examine now what happens between these 
opposite situations of the earth in its orbit. The , 
angle formed by the radius vector and the axis of 
the earth varies incessantly, while that formed by 
the axis and the orbit remains the same. At the 
situation midway between T and T', whicli we 
designate by f , the angle formed by the radius 
vector and the axis is neither acute, as at T, nor 
obtuse, as at T', but a right angle. Again, when 
the earth passes T' this angle diminishes, and 
when at t it is again a right angle; and again 
becomes acute between / and T. When the earth 
is at t' or t the radius vector is perpendicular to the 
axis ; and these epochs are called the vernal equinox 
and the autumnal equinox. 

The constant inclination of the axis of the earth 
to the plane of the ecliptic makes the sun appear to 



WONDERS OF THE HEAVENS. 



75 



us to describe a series of circles in passing from one 
tropic to another ; circles that he moves over again 
on his return toward the equator. Each of these 
apparent circles is the effect of our daily rotation ; 
and the passage from one circle to another, or the 
change in declination of the sun, is owing to our 
motion in the ecliptic. The time of the sun's 
meridian passage, or noon, is not exactly the middle 
of the day, except at midsummer and midwinter, i. e. 
at the solstices. By reason of the constant change 
of declination, the hour of the sun's rising and 
setting are not the same. At the vernal equinox 
the afternoon exceeds the forenoon by one and one 
Mh minutes; at the autumnal equinox the reverse 
takes place. 

The inhabitants of the equator (as we before 
stated) have the poles of the heaven in their 
horizon. All the circles described by the heavenly 
bodies are vertical 'and bisected by the horizon. 
The days and nights are equal through the whole 
year. The sun passes through their zenith twice 
a year, and its meridian altitudes when at the 
solstices is QQ° 32', — equal to the inclination of the 
earth's axis to the ecliptic. These altitudes in- 
crease as the equinoxes draw near. In the course 
of the year the shadows take all possible positions, 
now on one side of the equator, now on the other, 
six months toward the north, six toward the south. 
The shadows at noon, being directed to the pole, 
grow shorter and shorter until the sun reaches the 
equinoxes; then there are no shadows at noon. 
During our summer and spring these shadows 
are cast toward the south; during our winter and 
autumn toward the north. 

Properly speaking, they have no spring or 
autumn at the equator, but two summers and two 
winters. The first season is the most disagreeable, 
on account of the scorching heats and excessive 
rains. 

On 



account of the great 



heat of the regions 



between the tropics, this belt of the earth has 
received the name of the torrid zone. Yet it would 
appear, from recent observations made by intrepid 
travellers, who some years since explored the 
interior of Africa, and have made interesting dis- 



coveries there, that the torrid zone is not exempt 
from a considerable degree of cold. They tell us 
that " one of their younger companions perished 
with the severity of the cold." 

As we leave the tropics and advance toward the 
poles the phenomena change at every step. The 
length of the day increases in summer and shortens 
in winter in our latitude; the shadows of objects at 
noon being always toward the north. The zenith 
advances toward the poles as we advance, and the 
days of summer grow longer and longer, those of 
winter shorter and shorter. When we arrive at 
the distance of twenty-three and a half degrees 
from the north pole, we are on the polar circle, 
where the sun is above the horizon twenty-four 
hours at the summer solstice, and twenty-four hours 
below it, at the winter solstice. Nearer the pole 
it will remain longer above or below their horizon 
at the solstices; and finally, arrived at the pole, we 
shall have the sun six months above our horizon 
and six months below it ; and the year will consist 
of one day and one night, of equal duration. The 
parts of the earth within the polar circles are called 
frigid ov frozen zones; those between these circles 
and the tropics, temperate zones. 

These divisions, though matters of convention, 
are not altogether arbitrary. Their general tem- 
perature was the origin of their names. The cold 
is of longer continuance and more severe as we 
approach the frigid zone during the time when the 
sun is describing the opposite tropic; but when it 
describes the nearer tropic, the weakness of the 
oblique ray is compensated by the long duration of 
its action, since the sun is a long time above the 
horizon, and the temperature is much raised. 

Observers have found many causes that diminish 
a little the horror of the long night to which the 
Boreal inhabitants are exposed. From the nature 
of the atmosphere that surrounds the polar regions 
the slightest ray of light is refracted with a much 
greater intensity than in any other portion of the 
globe, and the day begins the moment the smallest 
portion of the sun's disc appears above the horizon : 
so that when the sun is below this plane, the polar 
regions may yet be lighted. The rapid decrease 



76 



WONDERS OF THE HEAVENS 



in the density of the air at small heights, owing to 
the constant congelation of the surface of the 
ground, is a cause which must tend to produce 
extraordinary refractions. This seems to be 
confirmed by the narration of three Hollanders. 
Having reached eighty-four degrees of north lati- 
tude, and being hemmed in by the ice, they were 
obliged to pass the winter at Nova Zembla. After 
three months of continual night, the cold having 
become extremely rigorous, the sun appeared an 
instant above the horizon at midday fourteen days 
sooner than they expected it in that latitude, and 
it continued after that day to rise higher and 
higher. If this narration be true, the refraction 
must have been equal to four degrees, which is 
enormous compared with its effects in our latitude, 
where it does not much exceed half a degree. 

Beside, the long nights of these regions are 
frequently interrupted by a certain splendid light 
suddenly appearing in the heavens, which we call 
Aurora Borealis. Of the two hemispheres, the 
northern seems to be less cold than the southern. 
The ice that surrounds its pole does not extend 
more than ten degrees of latitude ; while that of the 
antarctic pole extends twenty degrees. There are 
detached from the latter enormous ice islands, 
which float as far as sixty-five degrees, and even to 
fifty-five, which corresponds nearly with the latitude 
of the north of Ireland; and the most severe cold 
reigns in countries whose latitude differs but little 
from that of Scotland. Such is Terra del Fuego, 
which would seem to have been named in mockery 
the Land of Fire ; placed at the extremity of South 
America, it is covered with eternal snow. 

We shall now endeavor to illustrate what has 
been said by the following experiment and several 
plates, which, we trust, will make the subject plain 
to every reader. 

Take about seven feet of strong wire, and bend 
it into a circular form, which, being viewed ob- 
liquely, will appear elliptical. Place a lighted can- 
dle on a table, and having fixed one end of a silk 
thread to the north pole of a small terrestrial globe 
about three inches diameter, cause another person 
to hold the wire circle, so that it may be parallel 



to the table, and as high as the flame of the candle, 
which should be in or near the centre. Then, 
having twisted the thread towards the left, that by 
untwisting it may turn the globe round eastward, 
or contrary to the way that the hands of a watch 
move, hang the globe by the thread within this 
circle, almost contiguous to it ; and as the thread 
untwists, the globe (which is enlightened half round 
by the candle as the earth is by the sun) will turn 
round its axis, and the different places upon it will 
be carried through the light and dark hemispheres, 
and have the appearance of a regular succession of 
days and nights, as our earth has in reality by such 
a motion. As the globe turns, move your hand 
slowly, so as to carry the globe round the candle, 
keeping its centre even with the wire circle ; and 
you will perceive that the candle, being still per- 
pendicular to the equator, will enlighten the globe 
from pole to pole in its whole motion round the 
circle ; and that every place on the globe goes 
equally through the light and the dark, as it turns 
round by the untwisting of the thread, and there- 
fore has a perpetual equinox. The globe thus 
turning round represents the earth turning round its 
axis ; and the motion of the globe round the candle 
represents the earth's annual motion round the sun, 
and shows, that if the earth's orbit had no inclina- 
tion to its axis, all the days and nights of the year 
would be equally long, and there would be no dif- 
ferent seasons. But now, desire the person who 
holds the wire to hold it obliquely, raising one side 
just as much as he depresses the other, that the 
flame may be still in the plane of the circle ; and 
twisting the thread as before, that the globe may 
turn round its axis the same way as you carry it 
round the candle, that is, from west to east, let 
the globe down into the lowermost part of the wire 
circle, and if the circle be properly inclined, the 
candle will shine perpendicularly on the tropic of 
Cancer; oxidiihe frigid zone, lying within the arctic 
or north polar circle, will be all in the light, and 
will keep in the light, let the globe turn round its 
axis ever so often. From the equator to the north 
polar circle all the places have longer days and 
shorter nights ; but from the equator to the south 



WONDERS OF THE HEAVENS 



77 



polar circle just the reverse. The sun does not 
set to any part of the north frigid zone, as shown 
by the candle's shining on it, so that the motion 
of the globe can carry no place of that zone into 
the dark: and at the same time the south frigid 
zone is involved in darkness, and the turning of the 
globe brings none of its places into the light. If 
the earth were to continue in the like part of its 
orbit, the sun would never set to the inhabitants of 
the north frigid zone, nor rise to those of the south. 
At the equator it would be always equal day and 
night ; and as places are gradually more and more 
distant from the equator, towards the arctic circle, 
they would have longer days and shorter nights ; 
whilst those on the south side of the equator 
would have their nights longer than their days. In 
this case there would be continual summer on the 
north side of 'the equator, and continual winter on 
the south side of it. 

But as the globe turns round its axis, move your 
hand slowly forward, and the boundary of light and 
darkness will approach towards the north pole, and 
recede towards the south pole ; the northern places 
will go through less and less of the light, and the 
southern places through more and more of it; 
showing how the northern days decrease in length, 
and the southern days increase, whilst the globe 
proceeds. When the globe is at a mean state be- 
tween the lowest and highest parts of its orbit, and 
the candle is directly over the equator, the bounda- 
ry of light and darkness just reaches to both the 
poles, and all places on the globe go equally 
through the light and dark hemispheres, showing 
that the days and nights are then equal at all places 
of the earth, the poles only excepted; for the sun 
is then setting to the north pole, and rising to the 
south pole. 

Continue moving the globe forward; the north 
pole recedes still farther into the dark hemisphere, 
and the south pole advances more into the light, 
and when the candle is directly over the tropic of 
Capricorn, the days are at the shortest, and nights 
at the longest, in the northern hemisphere, all the 
way from the equator to the arctic circle; and the 
reverse in the southern hemisphere, from the equa- 



tor to the antarctic circle ; within which circles it 
is dark to the north frigid zone, and light to the 
south. 

Continue both motions ; the north pole advances 
towards the light, and the south pole recedes 
towards the dark ; the days lengthen in the north- 
ern hemisphere, and shorten in the southern ; and 
when the candle is again over the equator the days 
and nights will again be equal, and the north pole 
will be just coming into the light, the south pole 
going out of ii. 

Thus we see the reason why the days lengthen 
and shorten from the equator to the polar circles 
every year; why there is no day or night for 
several rotations of the earth within the polar 
circles ; why there is but one day and one night in 
the whole year at the poles ; and why the days and 
nights are equally long all the year round at the 
equator, which is always equally cut by the circle 
bounding light and darkness. 

The inclination of an axis or orbit is merely 
relative, because we compare it with some other 
axis or orbit which we consider as not inclined at 
all. Thus, our horizon being level to us, whatever 
place of the earth we are upon, we consider it as 
having no inclination ; and yet, if we travel ninety 
degrees from that place, we shall then have a 
horizon perpendicular to the former ; but it will 
still be level to us. 

Let us now illustrate the annual course of the 
earth round the sun ; its axis inclining twenty-three 
and a half degrees from a line perpendicular to the 
plane of its orbit, and keeping the same oblique 
direction in all parts of its annual course; or, as 
commonly termed, keeping always parallel to it- 
self. 




Let a, b, c, d, e,f, g, h be the earth in eight dif- 
ferent parts of its orbit, equidistant from one 
another ; N 5 its axis, N the north pole, s the south 



78 



WONDERS OF THE HEAVENS. 



pole, and S the sun, nearly in the centre of the 
earth's orbit. As the earth goes round the sun 
according to the order of the letters, abed, &c. 
its axis N s keeps the same obliquity.. When the 
earth is at a, its north pole inclines towards the 
sun, S, and brings all the northern places more 
into the light than at any other time of the year. 
But when the earth is at e, in the opposite time of 
the year, the north pole declines from the sun, 
which occasions the northern places to be more in 
the dark than in the light ; and the reverse at the 
southern places, as is evident by the figure. When 
the earth is either at c or g, its axis inclines neither 
to or from the sun, but lies sidewise to him; and 
then the poles are in the boundary of light and 
darkness ; and the sun, being directly over the 
equator, makes equal day and night at all places. 
When the earth is at Z), it is half way between the 
summer solstice and harvest equinox; when it is 
at d, it is halfway from the harvest equinox to the 
winter solstice; at /, half way from the winter 
solstice to the spring equinox ; and at h, half way 
from the spring equinox to the summer solstice. 

From this oblique view of the earth's orbit, let 
us suppose ourselves to be raised far above it, and 
placed just over its centre, S, looking down upon it 
from its north pole ; and as the earth's orbit differs 
but very little from a circle, we shall have its 
figure in such a view represented by the circle 
ABCDEFGH. The earth is shown in eight 
different positions in this circle, and in each posi- 
tion M is the equator, T the tropic of Cancer, U 
the arctic or north polar circle, and P the north 
pole, where all the meridians or hour-circles meet. 
As the earth goes round the sun, the north pole 
keeps constantly towards one part of the heavens, 
as it keeps in the figure towards the right hand 
side of the plate. (See page 79.) 

When the earth is at the beginning of the 
Balance, namely, on the 20th of March, the sun, 
S, as seen from the earth, appears in the opposite 
part of the heavens, the north pole is just coming 
into the light, and the sun is vertical to the equa- 
tor; which, together with the tropic of Cancer 
and arctic circle, are equally cut by the circle 



bounding light and darkness, coinciding with the 
six o'clock hour circle, and therefore the days and 
nights are equally long at all places ; for every 
part of the meridian ^E T L a comes into the light 
at six in the morning, and, revolving with the earth 
according to the order of the hour-letters, goes 
into the dark at six in the evening. There are 
twenty-four meridians or hour circles drawn on the 
earth in this figure, to show the time of sun rising 
and setting at different seasons of the year. 

As the earth moves in the ecliptic according to 
the order of the letters A B C D, &.c. the north 
pole comes more and more into the light; the 
days increase as the nights decrease in length, at 
all places north of the equator, JE; which is plain 
by viewing the earth at b on the 5 th of May. For 
then, the tropic of Cancer, T, is in the light from 
a little after five in the morning till' almost seven 
in the evening; the polar circle, U, from three till 
nine ; and a large track round the north pole, P, 
has day all the twenty-four hours, for many rota- 
tions of the earth on its axis. 

When the earth comes to c, on the 21st of June, 
its north pole inclines towards the sun, so as to 
bring all the north frigid zone into the light, and 
the northern parallels of latitude more into the 
light than the dark from the equator to the polar 
circle; and the more so as they are farther from 
the equator. The tropic of Cancer is in the light 
from five in the morning till seven at night, and 
the polar circle just touches the dark, so that the 
sun has onl}^ the lower half of his disc hid from the 
inhabitants on that circle for a few minutes about 
midnight, supposing no inequalities in the horizon, 
and no refractions. 

A bare view of the figure is enough to show, 
that as the earth advances, the north pole recedes 
towards the dark, which causes the days to de- 
crease and the nights to increase in length, till the 
earth comes to the beginning of the Ram, and then 
they are equal, as before; for the boundary of light 
and darkness cuts the equator and all its parallels 
equally, or in halves. The north pole then goes 
into the dark, and continues therein until the earth 
goes half way round its orbit ; or, from the 23d of 



WONDERS OF THE HEAVENS 



79 







80 



WONDERS OF THE HEAVENS 



September till the 20th of March. In the middle 
between these times, viz. on the 22d of December, 
the north pole is as far as it can be in the dark, 
which is twenty-three and a half degrees, equal to 
the inclination of the earth's axis from a perpendicu- 
lar to its orbit: and then the northern parallels 
are as much in the dark as they were in the light 
on the 21st of June; the winter nights being as 
long as the summer days, and the winter days as 
short as the summer nights. 

We have already spoken of the orbit of the earth. 
We shall, however, dwell a little on the nature of 
this curve which the earth annually describes. 

Mathematicians have proved that it is not a 
circle, as some have supposed, with the sun in its 
centre, but a curve, one of whose diameters is 
longer than the other, called an ellipse. The 
longest diameter we call the transverse or greater 
axis, which divides the figure into two equal parts 
in the direction of its greatest length. The diame- 
ter drawn at right angles to the greater axis is 
called the conjugate axis. This curve may be de- 
scribed by means of two points lying in the greater 
axis and equally distant from the central point; 
they are so situated that the sum of the lines drawn 
from each of them to any point of the curve is al- 
ways the same, and is equal to the longer axis. 

In the figure adjoining A P is the greater or 
transverse axis, C the central point, F and S are 
the/od, G H is the conjugate axis. The sujn of 




the lines S E, F E, drawn to any point of the curve, 
is the same, and equal to the transverse A P. Ap- 
plying this to the earth, S is the sun in one of the 
foci, E the earth passing from west to east along 
through G to A. The method of drawing the 
ellipse is very simple. Take a thread equal in 



length to the greater axis, and fasten its ends by 
two pins fixed in the points F, S. If now, with a pen 
or pencil, keeping the thread constantly stretched, 
we describe such a line as the confinement of the 
instrument allows, we shall form an elliptic curve. 
The distance of the foci from the central point C is 
called the eccentricity of the ellipse. 

The orbit of the earth is a similar curve, having 
the sun situated in or near one of its foci. The arc 
that the earth describes in this curve is not of 
equal length every day, but longer the nearer it is 
to the sun. 

By reason of this daily change of place to which 
the earth is subject, the apparent place of the sun 
is constantly changing. Thus, beside the change 
of declination which causes the seasons, it is appa- 
rently subject to a change in right ascension. It 
appears to remove a degree in the course of a day 
from the star with which it coincided at the begin- 
ning of that day. These retardations, accumulating 
every day, become at length so great, that the stars 
which passed the meridian with the sun at last pass 
this line long before, and the heavens appear en- 
tirely changed. When a star, which had for a time 
failed to be visible to us, appears in the east, in the 
morning twilight, it is said to rise heliacally; when 
it sets an hour after the sun it is said to set helia- 
cally. 

Those phenomena that happen at the instant of 
sunrise we distinguish by the epithet cosmical; and 
those that happen at the instant of sunset, achroni- 
cal. A planet is said to rise achronically when it 
rises at sunset and is visible the Avhole night. It 
rises cosmically when it rises exactly with the sun. 
Then it is not visible to our naked eyes for the 
whole of its course. 

As the heavenly bodies are not, in general, visi- 
ble to the naked eye unless they are distant about 
fifteen degrees from the sun, it follows that their 
rising cosmically precedes, by about fifteen days, 
their heliacal rising ; and that their heliacal setting 
precedes their achronical setting the same interval. 

The heliacal rising of the stars is important to be 
observed. It once served the agriculturists to fix 
the time of their various labors. But the position 



WONDERS OF THE HEAVENS 



81 



of the equinoxes having changed, the rules would 
likewise require change. 

The time in which the earth passes through the 
whole of its elliptical orbit, according to the most 
exact measure, is three hundred and sixty-five days 
five hours forty-eight minutes fifty-one seconds. 
We call this interval a tropical year, because it is 
determined by two successive passages of the sun 
over the same point of its apparent orbit ; as, for in- 
stance, the equinoctial or solstitial points. In the 
preceding figure the point P, in which the earth is 
nearest the sun, is called the perihelion ; the point A, 
diametrically opposite, in which the earth is farthest 
froin the sun, is called the aphelion. These two points 
taken together are called the apsides. The line A P, 
which joins them, is called the line of the apsides. 
In northern latitudes the earth is nearest the sun in 
winter and farthest from the sun in summer; — a fact 
which one not versed in astronomy at all would be 
far from supposing. 

What we have seen in the law of the centripetal 
force, viz. a choice guided by views of utility, and 
a choice of one law out of thousands which might 
equally have taken place, we see no less in the 
figure of the orbit. It was not enough to fix the 
law of centripetal force, though by the wisest 
choice ; for even under that law it was still possible 
for the earth to have moved in a path possessing so 
great a degree of eccentricity, as in the course of 
every revolution to be brought very near the sun 
and carried off to an immense distance from him. 
The comets actually move in orbits of this sort; 
and had the earth done so, instead of going round 
in an orbit nearly circular, the change from one 
extremity of temperature to another must have de- 
stroyed every animal and plant on its surface. 
Now the distance from the centre at which the 
earth shall set off, and the absolute force of attrac- 
tion at that distance, being fixed, the figure of its 
orbit (its being a longer or a rounder oval) depends 
upon two things, viz. the velocity with which, and 
the direction in which the earth were projected. 
And these, in order to produce a right result, must 



be both brought within certain narrow limits. One 
and only one velocity, united with one and only one 
direction, will produce a perfect circle. And the 
velocity must be nearly, but not exactly, the same, 
and the direction nearly, but not exactly, the same, 
to produce an orbit such as the earth has, viz. an 
ellipse with small eccentricity. The velocity and 
the direction must both be right. If the velocity 
were wrong, no direction can compensate for it; if 
the direction be in any considerable degree oblique, 
no velocity will produce the requisite orbit. 

Take, for example, the attraction of gravity at the 
surface of the earth. The force of that attraction 
being what it is, out of all the degrees of velocity, 
swift and slow, with which a ball might be shot off, 
none would answer the purpose of which we are 
speaking but that which was nearly five miles a 
second. If it were less, the body would not get 
round, but fall to the earth; if much greater, the 
body would describe a very eccentric orbit, a long 
ellipse, the disadvantage of which we have mention- 
ed above. If the velocity were equal to or exceed- 
ed seven miles a second, the ball would fly off from 
the earth and be never again heard of In like 
manner with respect to the direction; out of the in- 
numerable angles in which the ball might be sent 
off, (we mean angles formed with a line drawn to 
the centre,) none would serve but that which was 
nearly a right one ; out of the various directions in 
which the cannon must be pointed upwards or 
downwards, every one would fail but that which 
was exactly or nearly horizontal. The same holds 
true of the earth. Why then did the projectile 
velocity and direction of the earth happen to be 
those which would retain it in nearly a circular or- 
bit 1 Why not one of the infinite number of veloci- 
ties, one of the infinite number of directions, which 
would have made it approach much nearer to or 
recede much farther from the sun ? Such an exqui- 
site arrangement could only arise from the contri- 
vance and powerful influences of an intelligent, free, 
and most potent Agent, of a Being whose wisdom 
and power are infinite. 



11 



82 



WONDERS OF THE HEAVENS 



SECTION III. 

The horizon and its dip — The earth at first supposed a limited plane 
■ — Early reasoning to the contrary — Proof furnished by navigation 
— Objections caused by our ideas of weight — Answered — Conical 
figure of the earth's shadow — Other proofs — Different aspects of the 
heaven according to the position of the observer- — Time different 
in different places at the same absolute instant — Method of mea- 
suring an arc of the meridian — The earth an oblate spheroid — 
First meridian — Original constitution of the earth — Extent of the 
horizon proportioned to the height of the eye — Visible portion of 
the earth's surface — Temperature of the earth at its surface — In- 
ternal heat — Atmosphere — Reflections on the wisdom and know- 
ledge of the Creator — Diversities of the globe. 

In studying the earth, we are desh'ous, among 
other things, to form a conception of its shape and 
size. Now, an object cannot have shape and size 
unless it is limited on all sides by some definite out- 
line, so as to admit of our imagining it disconnected 
from other bodies, and existing insulated in space. 
The first rude notion we form of the earth is that 
of a flat surface, of indefinite extent in all directions 
from the spot where we stand, above which are the 
air and sky; below, to an indefinite profundity, 
solid matter. This is a prejudice to be got rid of, 
like that of the earth's immobility ; but it is one 
much easier to rid ourselves of, inasmuch as it 
originates only in our own mental inactivity, in not 
questioning ourselves where we will place a limit 
to a thing we have been accustomed from infancy 
to regard as immensely large ; and does not, like 
that, originate in the testimony of our senses un- 
duly interpreted. On the contrary, the direct 
testimony of our senses lies the other way. When 
we see the sun set in the evening in the west, and 
rise again in the east, as we cannot doubt that it is 
the same sun we see after a temporary absence, we 
must do violence to all our notions of solid matter, 
to suppose it to have made its way through the sub- 
stance of the earth. It must, therefore, have gone 
under it, and that not by a mere subterraneous 
channel; for if we notice the points where it sets and 
rises for many successive days, or for a whole year, 
we shall find them constantly shifting, round a very 
large extent of the horizon; and, besides, the moon 
and stars also set and rise again in all points of the 
visible horizon. The conclusion is plain : the earth. 



cannot extend indefinitely in depth downwards, nor 
indefinitely in surface laterally; it must have not 
only bounds in a horizontal direction, but also an 
under side, round which the sun, moon, and stars 
can pass ; and that side must, at least, be so far 
like what we see, that it must have a sky and sun- 
shine, and a day when it is night to us, and vice 
versa. 

Now, it is not on land (unless, indeed, on uncom- 
monly level and extensive plains) that we can see 
any thing of the general figure of the earth ; — the 
hills, trees, and other objects which roughen its 
surface, and break and elevate the line of the hori- 
zon, though obviously bearing a most minute pro- 
portion to the whole earth, are yet too considerable, 
with respect to ourselves and to that small portion 
of it which we can see at a single view, to allow of 
our forming any judgment of the form of the whole 
from that of a part so disfigured. But with the 
surface of the sea, or any vastly extended level 
plain, the case is otherwise. If we sail out of sight 
of land, whether we stand on the deck of the ship 
or climb the mast, we see the surface of the sea, 
not losing itself in distance and mist, but terminated 
by a sharp, clear, well defined line, or offing, as it is 
called, which runs all round us in a circle, having 
our station for its centre. That this line is really 
a circle, we conclude, first, from the perfect appa- 
rent similarity of all its parts ; and, secondly, from 
the fact of all its parts appearing at the same dis- 
tance from us, and that evidently a moderate one; 
and, thirdly, from this, that its apparent diameter, 
measured with an instrument called the dip sector, 
is the same (except under some singular atmospheric 
circumstances, which produce a temporary distor- 
tion of the outline) in whatever direction the mea- 
sure is taken, — properties which belong only to 
the circle among geometrical figures. If we ascend 
a high eminence on a plain, (for instance, one of the 
Egyptian pyramids,) the same holds good. 

Masts of ships, however, and the edifices erected 
by man, are trifling eminences compared to what 
nature itself affords ; iEtna, Teneriffe, Mowna Roa, 
are eminences from which no contemptible aliquot 
part of the whole earth's surface can be seen ; but 



WONDERS OF THE HEAVENS. 



83 



from these again — in those few and rare occasions 
when the transparency of the air will permit the 
real boundary of the horizon, the true sea-line, to 
be seen — the very same appearances are witnessed, 
but with this remarkable addition, viz. that the an- 
gular diameter of the visible area, as measured by 
the dip sector, is materially less than at a lower 
level, or, in other words, that the apparent size of 
the earth has sensibly diminished as we have re- 
ceded from its surface, while yet the absolute quanti- 
ty of it seen at once has been increased. 

The same appearances are observed universally, 
in every part of the earth's surface visited by man. 

A diagram will elucidate this. Suppose the 
earth to be represented by the sphere L H N Q, 



\ 



\ 



xi 




M 




lY 


:\ /I 


\^ 


\ 


1 

/ 


\ 

NX 


^^^^^1 


^ 


^ 




/ 7 


1 


yo" 








"v^ 


'^ 


\ 


10 


c, 




\ 


pi 



x^ 



G 



whose centre is C, and let A, G, M be stations at 
different elevations above various points of its sur- 
face, represented by c, g, ot, respectively. From 
each of them (as from M) let a line be drawn, as 
M N n, a tangent to the surface at N ; then will this 
line represent the visual ray along which the 
spectator at M will see the visible horizon ; and as 
this tangent sweeps round M, and comes suc- 
cessively into the positions M o, MPp, MQr/, 
the point of contact N will mark out on the surface 
the circle N P Q. The area of this circle is the 
portion of the earth's surface visible to a spectator 
at M, and the angle N M Q, included between the 



two extreme visual rays, is the measure of its appa- 
rent angular diameter. Leaving, at present, out 
of consideration the effect of refraction in the air 
below M, of which more hereafter, and which al- 
ways tends, in some degree, to increase that angle, 
or render it more obtuse, this is the angle measured 
by the dip sector. Now, it is evident, 1st, that as 
the point M is more elevated above m, the point 
immediately below it on the sphere, the visible 
area, i. e. the spherical segment or slice N P Q, 
increases; 2dly, that the distance of the visible 
horizon, or boundary of our view, from the eye, viz. 
the line M N, increases; and, 3dly, that the angle 
N M Q, becomes less obtuse, or, in other words, the 
apparent angular diameter of the earth diminishes, 
being nowhere so great as 180°, or two right an- 
gles, but falling short of it by some sensible quantity, 
and that more and more the higher we ascend. 
The figure exhibits three states or stages of eleva- 
tion, with the horizon, &c. corresponding to each, 
a glance at which will explain our meaning ; or, 
limiting ourselves to the larger and more distinct, 
M N P Q, let the reader imagine ra N M, M Q g 
to be the two legs of a ruler joined at M, and kept 
extended by the globe N w Q, between them. It is 
clear that as the joint M is urged home towards the 
surface, the legs will open, and the ruler will be- 
come more nearly straight, but will not attain per- 
fect straightness till M is brought fairly up to con- 
tact with the surface at m, in which case its whole 
length will become a tangent to the sphere at m, as 
is the line xy. This explains what is meant by 
the dip of the horizon. 

We propose to find how we can be placed in 
the centre of all the apparent celestial motions. 
The earliest idea entertained seems to have been, 
that the celestial dome touched the earth and was 
supported by it at the bounds of the horizon ; but 
ere long it was discovered that the earth, which 
had been supposed a plane and limited by the 
columns of Hercules, was much more extensive, and 
there began to be a doubt if there were any limits 
to it. It was perceived that men did not call it the 
same hour when at the same absolute instant they 
beheld a celestial phenomenon, as an eclipse of the 



84 



WONDERS OF THE HEAVENS. 



moon. Besides, the surface of the sea could not be 
a plane, for the navigator perceived, on approach- 
ing the shore, the highest summits first, and only in 
succession did he perceive lower situations. This 
could only be caused by the convexity of the sea. 
Even the best telescopes cannot bring within the 
view of a spectator on shore any thing but the 
highest parts of the mast of a very distant vessel : 
by its nearer approach the mast lengthens, and at 
last the hull of the vessel is distinguishable. If the 
sea were level, should we not see the hull before 
the mast? 

These appearances and that of a horizon or sea 
offing cannot arise from any inability in the eye to 
follow objects to a greater distance, or from atmos- 
pheric indistinctness, (if this were the case how 
could we see the same moon or stars placed at 
such infinitely greater distances ?) but from the 
curvature of the surface of the water. 
■ The convexity of the surface of the ocean once 
acknowledged, it is easy to come to a conclusion 
that the land also (with its irregularities) is rounded. 
Long voyages have confirmed this opinion. Navi- 
gators discover a new heaven, as it were, losing 
sight of ours, and perceiving the opposite part of 
the celestial sphere. Magellan made the first 
voyage round the world; and similar enterprises, 
often undertaken since, have demonstrated, that 
the earth has the form of a globe, isolated in space 
and surrounded by the heavens. If we had at first 
any difficulty in conceiving of this, it was because we 
mingled with it a false idea of weight; we demand- 
ed, why does not the earth, thus isolated, fall into 
the abyss ? How can it sustain itself and float in 
the void? How can those on the opposite side of 
the globe remain upon the soil? Have they not 
need of some force to retain them there ? But 
gravity, the cause of weight, is an attractive force 
resident in the earth itself. This retains every 
thing at the surface, and draws toward the centre 
of the earth every thing near the surface. The 
action of falling is toward this centre : our antipodes 
cannot be freed from this tendency, any more than 
ourselves. Beside, no resistance is requisite to keep 
the earth in this space, if there is not a power 



tending to draw it aside into some exterior region, 
having neither top nor bottom, which we are 
pleased to call a void. 

We have also a proof of the rotundity of the earth 
from the conical figure of the shadow cast by the 
globe on the side opposite the sun. This, however, 
must be left until we come to treat of eclipses. We 
find that the earth must be round from moving to 
different parts of the surface, and from observations 
of the pole-star. If it were a plane, whatever 
might be the situation of the observer, the angle, 
formed by the vertical with that directed to the 
north pole, would always be the same; since the 
pole being situated at an infinite distance, the rays 
would be parallel as well as the verticals. Again, 
the circles described by the stars would every- 
where have the same inclination to the horizon. 
But if the earth is a sphere, this no longer will 
happen, and we know that it does not happen. In 
advancing toward the regions in the direction of 
the pole-star, that star is perceived to rise more 
and more; and although the circles described by 
the stars have the same extent, yet to us, thus 
changing our places, they would be variously in- 
clined to the horizon. Some of the stars which set 
to us would not set were we to go farther north, 
and some in the south which rise to us would cease 
to rise. 

To persons situated between the equator and the 
pole the sphere is said to be oblique. To an inhabi- 
tant of the pole of the earth, the celestial pole would 
coincide with the zenith ; the plane of the horizon 
would coincide with the plane of the equator; the 
stars neither rise nor set, but continually describe 
circles, parallel to the horizon. To a person thus 
situated the sphere is said to be parallel. To an 
inhabitant at the equator, the poles are in the 
horizon, the stars describe vertical circles, and the 
sphere is said to be right. To him, all the stars 
are visible through half their circles, and those 
stars that are in the equinoctial, by turns, pass 
through his zenith. All places on the surface of 
the earth, situated in the same great circle passing 
through both poles and perpendicular to the equator, 
have the same meridian, and the same hour at the 



. 



WONDERS OF THE HEAVENS. 



85 



same instant. Those not situated in this circle 
count different hours at the same instant. Suppose 
a star is on the meridian of a place ; the inhabitants 
that are in another horary plane inclined to the 
first thirty degrees will have the same star in their 
meridian two hours before or two hours after the 
first mentioned place, according as their plane is 
east or west of the other. 

The sun would pass the meridians of these 
places, so that when it was twelve or midday at 
one of them it would be ten A. M. or two P. M. at 
the other. This difference of hours is very sensible 
even on short voyages. If we were to travel from 
Boston to Buffalo, we should find our watch a little 
more than half an hour too fast, if it went with 
precision and had been set to Boston time. When 
the sun is on the meridian of Boston, that is, when 
it is twelve o'clock, at Buffalo the sun would be 
east of the meridian. It would want thirty-one 
minutes of twelve ; while at Halifax, Nova Scotia, it 
would be about half an hour after noon. If we 
went entirely round the globe we should count a 
day, more or less, according as we went east or 
west; and could we advance westward with the 
same rapidity as the sun, we should pass entirely 
round, the globe without changing our time at all, 
nor should we see a sunset or sunrise during our 
progress. This day, to him who circumnavigates 
the globe, is divided into small portions, propor- 
tionate to each day's travel, while the traveller is 
constantly changing his meridian. Suppose a 
phenomenon observed at the same absolute instant 
of time by different observers, but under the same 
meridian ; it would of necessity be the same hour 
of the day ; but it would not be so to two observers 
situated under different meridians. By calculating 
the difference of time between the two places, and 
allowing fifteen degrees for each hour, we should 
have the angle the planes of the two meridians 
make with each other. If the phenomenon, for 
example, were observed here at twelve or midday; 
at another place, at ten A. M.; at a third, at three 
P. M.; the plane of the meridian of the first place 
would form with that of the second an angle of 
thirty degrees, and with that of the third an angle 



of forty-five degrees. The second place would be 
thirty degrees west of the first ; the third would be 
forty-five degrees east of the first, and seventy-five 
east of the second. 

This experiment, so easily performed, of different 
observers noting the time of some particular phe- 
nomenon, and which has been frequently repeated, 
has made known the figure of the earth. If two 




observers, and 0', under the same meridian, have 
at their zeniths, Z and Z', stars whose distance from 
the pole differs one degree, the difference of the 
heights of the pole-star above the horizon, that is, 
the angle C 0', will be also one degree. Let the 
distance 0' be measured, and let similar observa- 
tions be repeated elsewhere. It is evident that if 
we everywhere find the arc of one degree to con- 
tain an equal number of miles, the earth is per- 
fectly spherical. Nor need the points and 0' be 
under the same meridian, for geometry teaches us 
to calculate all the parts of the spherical surface 
after attaining a knowledge of some. 

Methods the best conceived and the most exact 
have been employed for this important operation 
by Picard, Bouguer, Mason, Mechain, Delambre, 
Roy, Kater, Mudge, Svanburg, Struve, &c. and they 
have not been able to find any difference in the 
lengths of arcs of one degree on the meridians, 
except the arcs measured be very distant. 

A degree measured in Sweden exceeds a degree 
at the equator by less than one thousand yards, or 
about 120th part, — a difference manifestly too small 



86 



WONDERS OF THE HEAVENS 



to be taken into account in merely settling the 
general form of the earth, which we may accord- 
ingly regard as a sphere. The dimensions of this 
sphere are easily found by geometry. We shall 
soon arrive at more definite conclusion on this 
subject. 

If at the place we conceive a plane passing 
through the zenith and the pole, this will be the 
meridian of that place. Remove now to a place, 0', 
in the same plane, and continue the meridian; re- 
peat these operations in several places one after 
the other, and the consecutive planes will cut the 
surface of the globe, forming a terrestrial meridian. 
Place a telescope at 0, which is your first station, 
and direct it to 0', your second station, where a 
signal is to be placed, as also at the first station. 
Remove your instruments to 0' and direct your 
observation back to 0, and then forward to a third 
point, which will be your third station, and so on. 
The operations, continued as far as you please, will 
give an arc of the meridian, which is only the first 
direction continued and curved, without departing 
from the same vertical plane. 

The irregularities of the earth prevent us from 
measuring this arc exactly ; but with the aid of a 
base line, and a series of triangles whose angles are 
measured by instruments, we can calculate the 
length of the arc of the meridian which connects the 
extreme stations with the same precision as if it 
had been directly measured. We should find that 
the curve very nearly, but not exactly, coincided 
with the arc of a circle, since the globe is a little 
different from a sphere. It has been found that 
the lengths of the arcs of one degree go on increas- 
ing from the equator to the poles. If we regard 
the terrestrial meridian as composed of a series of 
arcs of circles of different radii, placed with their 
extremities joining, since the longest arc of one 
degree must be at the pole and have the longest 
radius, the radii increase from the equator to the 
pole. The verticals cross each other in different 
points, and the more distant from the surface at the 
poles than at the equator; that is, the earth is less 
convex at the poles. The earth is a little different 
from a sphere; it is a spheroid flattened at the poles. 




Although we suppose the small inequalities Vv^hich 
form the mountains removed, there would be found 
but little difference between the meridian curves 
and ellipses. We can find in works of Geodesy 
all the reasonings that serve to prove, that the earth 
is an ellipsoid of revolution about its smaller axis, 
which is that of the poles. It is by comparing the 
results of observations with formulas of the dimen- 
sions of this body that we succeed in verifying this 
conclusion, in finding the lengths of the arcs, the 
flatness at the poles, the distance from the pole to 
the equator, and, in fine, all parts of our spheroid. 
The flattening at the poles has been differently 
estimated, from ^l^ to 3^^; a mean between the 
two, ^i-^, cannot be far from the truth. An arc then 
of a degree taken under the equator is exceeded by 
an arc at the pole by -^^^ of its length. The radius 
of curvature at the equator is also less, by the same 
quantity, than the radius at the pole, since arcs of 
the same number of degrees in different circles are 
to each other as their radii. We have supposed 
the inequalities of surface removed, but in truth 
the most elevated mountains are but very small 
eminences compared to the whole mass, smaller 
than the asperities on the skin of an orange com- 
pared to the whole fruit. Mount Blanc, the highest 
mountain in Europe, is only elevated 15,665 feet 
above the level of the sea; Chimborazo, in Peru, 
is only 21,441 feet above the sea; finally, Dhawa- 
lageri, the highest peak of the Himalays, in Thibet, 
and the highest summit on the globe, is but 25,669 
feet above the sea. If, then, we represent the earth 
by a globe of two feet radius, the mountains would 
be scarcely perceptible inequalities on its surface. 

The whole surface of the earth is about ttvo hun- 
dred millions of square miles; three quarters of 
which are covered with water, and scarcely half of 
the remainder is habitable. 

To determiine the position of any point, P, on the 
surface of the earth, we draw through P and the 
poles, N and S, a circle perpendicular to the equa- 
tor, E R. The distance P E of the point P from the 
equator is called its latitude. If we conceive a 
plane, A, parallel to the equator, it will cut the 
earth in a small circle, all whose points will have 



WONDERS OF THE HEAVENS 



87 



the same latitude, E or A R, or the same distance 
fiom the equator. The points of this small circle 




are the only points that can have the same degree 
of latitude, if we except those of a similar small 
circle drawn at an equal distance on the other side 
of the equator; and in speaking of a place it is 
necessary not only to indicate the degrees, but if it 
be situated toward the north or the south pole. 

The latitude of a place is always a number of 
degrees, that, added to the distance of the zenith of 
that place from the nearest pole, will make ninety 
degrees, and consequently is equal to the arc which 
measures the elevation of the pole above the hori- 
zon. And as these arcs can be measured in the 
heaven, we can determine it easily for any place, 
and consequently determine the latitude of that 
place. The distance of any place from the equator 
(its latitude) is equal to the elevation of the pole or the 
inclination of the earth's axis to the horizon of that 
place. It remains to distinguish from each other 
the different points of the circle A. Conceive 
through the point B of the equator another meridian, 
S B N, to be drawn : B N E, the angle that it makes 
with the first meridian, SEN, is measured by the 
arc B E of the equator intercepted by it. This arc 
B E expressed in degrees or in time is called the 
longitude of the point. 

The place of the second meridian is evidently 



determined by the arc B E, provided it is stated on 
which side of the first meridian it is situated, to the 
right or left, to the east or west. This second 
meridian being thus determined, the point C is also 
determined. 

The position of the first meridian is arbitrary. 
Nations have not been able to agree upon one. 
Each prefer the meridian of its own capital city. 
In France they use the meridian of Paris. The 
English use that of London, or, which is nearly the 
same, Greenwich, where the royal observatory is 
situated. And some of our countrymen have been 
jealous enough to use the meridian of Washington, 
as if it were of so much importance to count from 
our capital, as that all the world should agree upon 
one first meridian. 

To determine the longitude of a place, we em- 
ploy the method before explained, which consists 
in observing with care the precise instant of a 
celestial phenomenon, as an eclipse of the moon. 
If the observation were made in two places either 
situated or not under the same parallel to the 
equator, the difference of time at the instant of the 
observations, reduced to degrees, (fifteen degrees to 
the hour) will give the angles of the two meridians 
or the arc, that is, the longitude. That place will 
be east of the other at which the time counted was 
greatest, and vice versa. 

When we consider the figure of the earth and 
the law of its increase in density from the surface 
to the centre, we are disposed to believe that in 
its orio:inal constitution it was not so solid as at 
present; for if it were at first in a less solid state, 
its parts, being more subject to the power of at- 
traction and centrifugal force, would more readily 
assume the form we find it possesses. 

Imagine a bent tube, one branch of which, lying 
in the axis of rotation, might represent half the 
polar diameter, the other being in the direction of 
the radius of the earth's equator. Fill this siphon, 
open at both ends, wdth a liquid, and impart to it a 
motion similar to the rotation of the earth. The 
column in the direction of the polar diameter, obey- 
ing the action of gravity only, while the column in 
the equatorial radius was acted upon by the cen- 



88 



WONDERS OF THE HEAVENS 



trifugal force also, the polar column would sink 
enough to compensate for the diminution of weight 
in the equatorial column, and the liquid in the latter 
would rise in the same proportion, in order to 
restore the equilibrium in the two branches. 

Every one who has passed a little while at the 
sea-side is aware that objects may be seen perfectly 
well beyond the offing or visible horizon, but not 
the whole of them. We only see their upper parts. 
Their bases, where they rest on or rise out of the 
water, are hid from view by the spherical surface 
of the sea, which protrudes between them and our- 
selves. Suppose a ship, for instance, to sail direct- 
ly away from our station; at first, when the. dis- 
tance of the ship is small, a spectator, S, situated 
at some certain height above the sea, sees the 
whole of the ship, even to the water line where it 




have prevented an equally perfect view of the 
whole. 



rests on the sea, as at A. As it recedes it dimi- 
nishes, it is true, in apparent size, but still the ivhole 
is seen down to the water line, till it reaches the 
visible horizon at B. But as soon as it has passed 
this distance, not only does the visible portion still 
continue to diminish in apparent size, but the hull 
begins to disappear bodily, as if sunk below the 
surface. When it has reached a certain distance, 
as at C, its hull has entirely vanished, but the masts 
and sails remain, presenting the appearance c. But 
if, in this state of things, the spectator quickly as- 
cends to a higher station, T, whose visible horizon 
is at D, the hull comes again in sight; and when 
he descends again he loses it. The ship still reced- 
ing, the lower sails seem to sink below the water, 
as at d, and at length the whole disappears : while 
yet the distinctness with which the last portion of 
the sail d is seen is such as to satisfy us, that were 
it not for the interposed segment of the sea, 
ABODE, the distance T E is not so great as to 






In this manner, therefore, if we could measure 
the heights and exact distance of two stations which 
could barely be discerned from each other over the 
edge of the horizon, we could ascertain the actual 
size of the earth itself: and, in fact, were it not for 
the effect of refraction, by which we are enabled to 
see in some small degree round the interposed seg- 
ment, (as will be hereafter explained,) this would be 
a tolerably good method of ascertaining it. Sup- 
pose A and B to, be two eminences, whose perpen- 




dicular heights A a and B b (which, for simplicity, 
we will suppose to be exactly equal) are known, as 
well as their exact horizontal interval aJ) b, by 
measurement ; then it is clear that D, the visible 
horizon of both, will lie just half-way between them, 
and if we suppose aD b to be the sphere of the 
earth, and C its centre in the figure C D 6 B, we 
know D b, the length of the arc of the circle be- 
tween D and b, — viz. half the measured interval, 
and b B, the excess of its secant above its radius — 
which is the height of B, — data which, by the solu- 
tion of an easy geometrical problem, enable us to 
find the length of the radius DC. If, as is really 
the case, we suppose both the heights and distance 
of the stations inconsiderable in comparison with 



WONDERS OF THE HEAVENS. 



89 



the size of the earth, the solution alluded to is con- 
tained in the following proposition: — 

The earth's diameter bears the same proportion to the 
distance of the visible horizon from the eye as that dis- 
tance does to the height of the eye above the sea level. 

When the stations are unequal in height, the 
problem is a little more complicated. 

Although, as we have observed, the effect of re- 
fraction prevents this from being an exact method 
of ascertaining the dimensions of the earth, yet it 
will suffice to afford such an approximation to it as 
shall be of use in the present stage of the reader's 
knowledge, and help him to many just conceptions, 
on which account we shall exemplify its application 
in numbers. Now, it appears by observation, that 
two points, each ten feet above the surface, cease 
to be visible from each other over still water, and 
in average atmospheric circumstances, at a distance 
of about eight miles. But ten feet is the 528th 
part of a mile, so that half their distance, or four 
miles, is to the height of each as 4 X 528 or 2112: 1, 
and therefore in the same proportion to four miles 
is the length of the earth's diameter. It must, 
therefore, be equal to 4x2112=8448, or, in 
round numbers, about 8,000 miles, which is not 
very far from the truth. 

We have before likened the inequalities on the 
earth's surface, arising from mountains, valleys, 
buildings, &-c. to the roughnesses on the rind of an 
orange, compared with its general mass. The 
comparison is quite free from exaggeration. The 
highest mountain known does not exceed five miles 
in perpendicular elevation: this is only one 1600th 
part of the earth's diameter; consequently, on a 
globe of sixteen inches in diameter, such a moun- 
tain would be represented by a protuberance of no 
more than one hundredth part of an inch, which is 
about the thickness of ordinary drawing-paper. 
Now as there is no entire continent, or even any 
very extensive tract of land, known, whose general 
elevation above the sea is any thing like half this 
quantity, it follows, that if we would construct a 
correct model of our earth, with its seas, continents, 
and mountains, on a globe sixteen inches in diame- 
ter, the whole of the land, with the exception of a 



few prominent points and ridges, must be compris- 
ed on it within the thickness of thin writing paper ; 
and the highest hills would be represented by the 
smallest visible grains of sand. 

The deepest mine existing does not penetrate 
half a mile below the surface : a scratch, or pin- 
hole, duly representing it, on the surface of such a 
globe as our model, would be imperceptible without 
a magnifier. 

The greatest depth of sea, probably, does not 
much exceed the greatest elevation of the conti- 
nents; and would, of course, be represented by an 
excavation, in about the same proportion, into the 
substance of the globe : so that the ocean comes to 
be conceived as a mere film of liquid, such as, on 
our model, would be left by a brush dipped in color 
and drawn over those parts intended to represent 
the sea : only, in so conceiving it, we must bear in 
mind that the resemblance extends no farther than 
to proportion in point of quantity. The mechanical 
laws which would regulate the distribution and 
movements of such a film, and its adhesion to the 
surface, are altogether different from those which 
govern the phenomena of the sea. 

Lastly, the greatest extent of the earth's surface 
which has ever been seen at once by man, was that 
exposed to the view of MM. Biot and Gay-Lussac, 
in their celebrated aeronautic expedition to the 
enormous height of 25,000 feet, or rather less than 
five miles. To estimate the proportion of the area 
visible from this elevation to the whole earth's sur- 
face, we must have recourse to the geometry of the 
sphere, which informs us that the convex surface 
of a spherical segment is to the whole surface of 
the sphere to which it belongs as the versed sine or 
thickness of the segment is to the diameter of the 
sphere ; and further, that this thickness, in the case 
we are considering, is almost exactly equal to the 
perpendicular elevation of the point of sight above 
the surface. The proportion, therefore, of the 
visible area, in this case, to the whole earth's sur- 
face, is that of five miles to 8000, or 1 to 1600. 
The portion visible from ^tna, the Peak of Tene- 
riffe, or Mowna Roa, is about one 4000th. 

As we cannot grasp the earth, nor recede from 




90 



WONDERS OF THE HEAVENS 



it far enough to view it at once as a whole, and 
compare it with a known standard of measure in 
any degree commensurate to its own size, but can 
only creep about upon it, and apply our diminutive 
measm'es to comparatively small parts of its vast 
surface in succession, it becomes necessary to sup- 
ply, by geometrical reasoning, the defect of our 
physical powers, and from a delicate and careful 
measurement of such small parts to conclude the 
form and dimensions of the whole mass. This 
would present little difficulty, if we were sure the 
earth were strictly a sphere, for the proportion of 
the circumference of a circle to its diameter being 
known, (viz. that of 3-1415926 to 1-0000000,) we 
have only to ascertain the length of the entire cir- 
cumference of any great circle, such as a meridian, 
in miles, feet, or any other standard units, to know 
the diameter in units of the same kind. Now the 
circumference of the whole circle is known as soon 
as we know the exact length of any aliquot part of 
it, such as one degree or o^h part ; and, this 
being not more than about seventy miles in length, 
is not beyond the limits of very exact measurement, 
and could, in fact, be measured (if we knew its exact 
termination at each extremity) within a very few 
feet, or, indeed, inches, by methods presently to be 
particularized. 

Supposing, then, we were to begin measuring 
with all due nicety from any station, in the exact 
direction of a meridian, and go measuring on, till 
by some indication we were informed that we had 
accomplished an exact degree from the point we set 
out from, our problem would then be at once re- 
solved. It only remains, therefore, to inquire by 
what indications we can be sure, 1st, that we have 
advanced a;2 exact degree; and, 2dly, that we have 
been measuring in the exact direction of a great 
circle. 

Now, the earth has no landmarks on it to indicate 
degrees, nor traces inscribed on its surface to guide 
us in such a course. The compass, though it 
affords a tolerable guide to the mariner or the 
traveller, is far too uncertain in its indications, and 
too little known in its laws, to be of any use in 
such an operation. We must, therefore, look out- 



wards and refer our situation on the surface of our 
globe to natural marks, external to it, and which are 
of equal permanence and stability with the earth 
itself. Such marks are afforded by the stars. By 
observations of their meridian altitudes, performed 
at any station, and from their known polar distances, 
we conclude the height of the pole ; and since the 
altitude of the pole is equal to the latitude of the 
place, the same observations give the latitudes of 
any stations where we may establish the requisite 
instruments. When our latitude, then, is found to 
have diminished a degree, we know that, provided 
we have kept to the meridian, we have described one 
three hundred and sixtieth part of the earth's cir- 
cumference. 

The direction of the meridian may be secured at 
every instant by observations, and although local 
difficulties may oblige us to deviate in our measure- 
ment fi'om this exact direction, yet, if we keep a 
strict account of the amount of this deviation, a 
very simple calculation will enable us to reduce 
our observed measure to its meridional value. Such 
is the principle of the measurement of an arc of the 
meridian. 

Let N A B D E F represent a meridional section 
of the earth, C its centre, and N A, B D, G E, arcs 



n 


a 


V 


A 




^ 


A 


-mL 






^ 








\ 


1/ 


\ 




..--'■' 


'^f 


^..., 


\a 


? 


""---.. "^ 


/ 


^^I^" z; 


/ 


c 



of a meridian, each corresponding to one degree 
of difference of latitude, or to one degree of varia- 
tion in the meridian altitude of a star, as referred 
to the horizon of a spectator travelling along the 
meridian. Let w N, c A, 6B, c?D, gG, eE, be the 
respective directions of the plumli-line at the sta- 
tions N, A, B, D, G, E, of which we will suppose N 
to be at the pole and E at the equator ; then will the 



WONDERS OF TPIE HEAVENS 



91 



tangents to the surface at these points respectively 
be perpendicular to these directions ; and, conse- 
quently, if each pair, viz. n N and a A, 6 B and d D, 
g G and eE, be prolonged till they intersect each 
other, (at the points x, y,z,) the angles N a; A, B yT>, 
G0E, will each be one degree, and, therefore, all 
equal ; so that the small curvilinear arcs N A, B D, 
G E, may be regarded as arcs of circles of one de- 
gree each, described about x, y, z, as centres. 
These are what in geometry are called centres of 
curvature, and the radii x N or 5: A, ?/B or ?/D, 
2r G or E, represents radii of curvature, by which 
the curvatures at those points are determined and 
measured. Now, as the arcs of different circles, 
which subtend equal angles at their respective 
centres, are in the direct proportion of their radii, 
and as the arc N A is greater than B D, and that 
again than G E, it follows that the radius N x must 
be greater than B y, and B y than E z. Thus it 
appears that the mutual intersections of the plumb- 
lines will not, as in the sphere, all coincide in one 
point, C, the centre, but will be arranged along a 
certain curve, xyz, (which will be rendered more 
evident by considering a number of intermediate 
stations.) To this curve geometers have given the 
name of the evolute of the curve N A B D G E, from 
whose centres of curvature it is constructed. 

In the flattening of a round figure at two opposite 
points, and its protuberance at points rectangularly 
situated to the former, we recognise the distinguish- 
ing feature of'the elliptic form. Accordingly, the 
next and simplest supposition that we can make 
respecting the nature of the meridian, since it is 
proved not to be a circle, is, that it is an ellipse, or 
nearly so, having N S, the axis of the earth, for its 
shorter, and E F, the equatorial diameter, for its 
longer axis ; and that the form of the earth's sur- 
face is that which would arise from making such a 
curve revolve about its shorter axis, N S. This 
agrees well with the general course of the increase 
of the degree in going from the equator to the pole. 
In the ellipse, the radius of curvature at E, the 
extremity of the longer axis is the least, and at that 
of the shorter axis, the greatest it admits, and the 
form of its evolute agrees with that here represented. 



Assuming, then, that it is an ellipse, the geometri- 
cal properties of that curve enable us to assign the 
proportion between the lengths of its axes which 
shall correspond to any proposed rate of variation 
in its curvature, as well as to fix upon their abso- 
lute lengths, corresponding to any assigned length 
of the degree in a given latitude. Without trou- 
bling the reader with the investigation, it will be 
sufficient to state that the lengths which agree on 
the whole best with the entire series of meridional 
arcs which have been satisfactorily measured, are 
as follows : — 



Greater or equatorial diameter 
Lesser or polar diameter 
Difference of diameters, or polar com- 
pression 
Equatorial circumference 



Feet. Miles. 

= 4] ,847,426 =7925-648 
= 41,707,620=7899-170 

= 139,806= 26-478 

= = 24-899 



One of the most curious labors, of the present 
age, we owe to the energy and perseverance of 
Humboldt. It is an inquiry into the laws, which 
seem to exist in the distribution of organized matter 
over the surface of the earth. By measuring the 
elevation above the level of the sea of various 
places, and of the highest mountains of the earth, 
and by comparing all these measures together, he 
has found the localities in which certain plants de- 
light. For instance, the cinchona, or Jesuit's bark, 
has been discovered only in a certain zone, whose 
situation he determined. The same laws are appli- 
cable also to animals, whose more perfect organiza- 
tion and immediate dependence on physical causes 
would seem to free them from such laws. 

For example, in South America, observers have 
remarked, according to their assertions, on the 
parallel corresponding to the latitude of New Hol- 
land, animals whose organization presents very re- 
markable similarities to that of the echidnas,* which 

* This animal and the duck-bill platypus are the only genera of a 
peculiar tribe called monotrema. They partake of the triple form of 
a quadruped, bird, and reptile ; having the body of an otter, the legs 
of a tortoise, the wings and beak of a bird. There is a spur on the 
hind leg of the male, that emits an acrid humor. The legs are short, 
and end in five toes. The body is covered with fur, mixed with 
spines, like porcupine's quills. The animal can roll up his body, like 
the porcupine, and assume a spherical form. The echidna is tooth- 
less, has a small and conical head, very small eyes, a tongue capable 
of being elongated and thrown out like those of the chameleon and 
the woodpecker. 



92 



WONDERS OF THE HEAVENS 



exist in the latter country, and which are, without 
doubt, among the number of those whose strange 
organization merits the particular attention of the 
most learned zoologists. It would seem then, ac- 
cording to these observations, that such a combina- 
tion of organs can only be produced in certain 
determinate places. These curious results have 
induced philosophers to seek out their causes, and 
they regard the difference of temperature in the 
various countries of the earth as the most probable 
cause of their production, as well as the most im- 
portant. 

But whence originates this temperature of the 
earth ? Is it the sun that develops it? Some have 
been of this opinion, which is supported by the 
regularity observable in the phenomena of the uni- 
verse. Still, some facts seem to prove that the 
prolonged action of the sun is not the sole cause of 
the earth's temperature. It is a result of experi- 
ence, that at the bottom of wells a hundred feet 
deep the temperature remains uniform and invaria- 
ble; and ice that covers, throughout the year, the 
summits of certain mountains, is constantly melting 
at their base, and supplying streams of living wa- 
ter, that continue to flow during the winter. The 
earth, therefore, seems to possess a peculiar heat, 
independent of that which it receives from the sun. 
Some persons, on a consideration of the above facts, 
have thought that at a time very distant the earth 
was in a state of incandescence, (white heat;) that 
by degrees its surface cooled, until it reached its 
present temperature, the centre still retaining a 
greater heat, which they have called the central 
heat; and that this produces the effects mentioned 
above. 

The following extract on this subject is from one 
of professor Hitchcock's geological lectures. 

In regard to the central or internal heat of the 
earth, the first question is, has it disappeared ? Is 
there -any evidence of its existence now? The 
arguments in favor of its presence are, in the first 
place, experiments made in mines and other deep 
parts of the globe, in France, England, Switzerland, 
Peru, Mexico, &c. It is found that the heat in- 
creases as you descend below the surface. From 



three hundred experiments, (indeed many more 
than that,) made with a thermometer, upon the air 
at different depths, upon the water, and in the solid 
rock, with great care and exactness, all geologists 
agree that the heat rapidly increases as you de- 
scend. In Europe the increase is one degree of 
Fahrenheit for every twenty-four feet ; in America 
one degree for every seventy-two feet ; making the 
average for the whole globe about one degree for 
every forty-six feet. Analogy therefore leads us 
to infer very confidently that there is a continual 
increase to the centre. Taking the foregoing pro- 
portions, and at the depth of sixty miles, the rocks 
exist in a state of fusion, and at the depth of one 
and a half miles water would boil. The heat at 
the centre would thus equal 450,000 degrees of 
Fahrenheit. But it is asked, why then does not 
the ocean boil, it being much more than one and a 
half miles deep in some place, instead of growing 
cooler, as it actually does. The answer is, that 
when water is subjected to heat, the hottest is al- 
ways at the surface, because the particles are 
lighter, and the cold, being heavier, descends. 
Another answer is found in the suggestion, that the 
crust of the earth beneath the deepest part of the 
ocean may be equally thick as in other parts, but 
more depressed or indented. A map was exhibited, 
in which the crust of the globe bears about the 
same proportion to the whole earth as the rind of 
an orange to the whole pulp, or as sixty miles to 
eight thousand, the diameter of the earth, all within 
being liquid fire. Another objection made to the 
theory is, that as the melted mass is growing 
cooler, our climate would thus become cooler all 
over the globe. But a celebrated French geologist 
has demonstrated that the climate depends upon 
the sun, and that the internal heat now can have 
no perceptible effect. The experiment, by way of 
illustration, can be made with a red-hot cannon 
ball. At first it cools rapidly, but as soon as an. 
external crust is formed it cools very slowly. By 
the aid of fluxions he has mathematically demon- 
strated, that the temperature of the earth at the 
surface cannot be varied more than a one hundred 
and fiftieth part of a degree for two thousand years, 



WONDERS OF THE HEAVENS 



93 



and that it is not one fifteenth of a degree warmer 
with the internal fires than if the central parts were 
ice instead of heat: also, that the internal heat now 
escaping from the earth would not melt ice six feet 
thick at the surface in one hundred years. Dr. 
Bowditch, one of the first mathematicians in the 
world, has pronounced the demonstration complete 
and perfect. Another answer to the objection is 
found in the fact that there has actually been a 
change in the temperature of the globe. 

Without discussing further the validity of this 
hypothesis, we think that it is extremely probable, 
that the earth has of itself a heat that is suscepti- 
ble of variation, from causes with which we are as 
yet unacquainted. Since Galvani and Volta, by 
their discoveries, have proved that there cannot 
exist two bodies of a different nature without their 
developing electricity and heat, who can suppose 
that the earth, into the composition of which enters 
such a multitude of different bodies, and which is 
consequently traversed by incessant currents of 
active electricity, is incapable of possessing a heat 
of its own? 

Still, it is reasonable to consider the sun as the 
principal source of terrestrial heat. This last is 
dissipated insensibly, by radiating into space, and 
the more rapidly the more the temperature is 
raised; and as there is a certain equilibrium be- 
tween the heat that comes annually from the sun 
and that which is annually dissipated, the tempera- 
ture of the earth ought to remain constant. The 
places on the globe not receiving the same quantity 
of heat, on account of their different situations and 
the obliquity with which the sun's rays fall on them, 
ought to be variable in their temperature. These 
observations are confirmed by experience. In cer- 
tain parts of Siberia the earth never thaws, while 
in Egypt the Fahrenheit* thermometer would indi- 
cate seventy-one degrees at more than two hun- 
dred feet below the surface. At an intermediate 
place, cellars preserve constantly the temperature 
of fifty-four degrees. The temperature of our 

* Bailey says the temperature of twenty-two degrees by the centi- 
grade thermometer, reduced to degrees of Fahrenheit by multiplying 
by nine, dividing by five, and adding thirty -two to the quotient. 



globe, observed near its surface, would be found to 
decrease from the equator to the poles ; the law of 
this decrease has not yet been discovered. We 
shall not here recount the causes of the difference 
of temperature at various places. They are ex- 
tremely numerous, and constitute topics more 
suitable to physical geography than to this work. 

The atmosphere, that gaseous fluid which sur- 
rounds us, is composed of various substances, and 
is the cause of a thousand phenomena. It contains 
water in a state of vapor, which does not destroy 
its transparency, and water in suspension, which 
forms clouds and mists. The air diminishes in 
density as we ascend, and when we arrive at any 
considerable elevation we are made aware, by 
many uneasy sensations, of an insufficient supply. 
Acosta, in his relation of a journey among the 
mountains of Peru, states, that he and his com- 
panions were surprised with such extreme pangs of 
straining and vomiting, casting up blood, and with 
so violent a distemper, that they would undoubtedly 
have died had they remained two or three hours 
longer in that elevated situation. Count Zambecari 
and his companions, who ascended in a balloon to 
a great height, found their hands and feet so 
swelled that it was necessary for a surgeon to make 
incisions in the skin. A calculation, founded on 
our knowledge of the properties of air, is sufficient 
to show that at an altitude not exceeding the hun- 
dredth part of the earth's diameter, the rarefaction 
must be so excessive, that the most delicate means 
we possess of ascertaining the existence of air 
would fail to afford the slightest indication of its 
presence. For all practical purposes, therefore, 
we may consider those regions which are more dis- 
tant above us than the hundredth part of the earth's 
diameter (or seventy-five miles) as void of air, and, 
of course, of clouds, they being only vapor con- 
densed and floating in the air^ and sustained by it. 
Now the greatest height at which clouds ever exist 
seems not to exceed ten miles. We may consider, 
then, the atmosphere, with its clouds, as a coating 
to the earth, bearing about the same proportion to 
the globe as the downy skin of a peach does to the 
fruit within. Still, the atmosphere is one of the 



94 



WONDERS OF THE HEAVENS. 



■ most essential appendages to the globe we inhabit, 
and exhibits a most striking scene of divine skill and 
omnipotence. The term atmosphere is applied to 
the whole mass of fluids, consisting of air, vapors, 
electric fluid, and other matters, which surround 
the earth to a certain height. This mass of fluid 
matter gravitates to the earth, revolves with it in 
its diurnal rotation, and is carried along with it in 
its course round the sun every year. From experi- 
ments made by the barometer, it has been ascer- 
tained, that it presses with a weight of about fifteen 
pounds on every square inch of the earth's surface; 
and, therefore, its pressure on the body of a middle- 
sized man is equal to about thirty-two thousand 
pounds, or fourteen tons avoirdupois, — a pressure 
which would be insupportable, and even fatal, 
were it not equal in every part, and counter- 
balanced by the spring of the air within us. The 
pressure of the whole atmosphere upon the earth is 
computed to be equivalent to that of a globe of lead 
sixty miles in diameter, or about 5,000,000,000,- 
000,000 tons ; that is, the whole mass of air which 
surrounds the globe compresses the earth with a 
force or power equal to that of five thousand millions 
of millions of tons. This amazing pressure is, how- 
ever, essentially necessary for the preservation of 
the present constitution of our globe, and of the 
animated beings which dwell on its surface. It 
prevents the heat of the sun from converting water, 
and all other fluids on the face of the earth, into 
vapor; and preserves the vessels of all organized 
beings in due tone and vigor. Were the atmos- 
pherical pressure entirely removed, the elastic fluids 
contained in the finer vessels of men and other 
animals would inevitably burst them. 

Whatever evidences of contrivance and design 
the celestial globes may exhibit, it is not in the 
heavens that the most striking displays of divine 
wisdom can be traced by the inhabitants of our 
world. It is only a few general relations and adapta- 
tions that can be distinctly perceived among the 
orbs of the firmament; though, in so far as we are 
able to trace the purposes which they subserve, the 
marks of beauty, order, and design, are uniformly 
apparent. But we are placed at too great a dis- 



tance from the orbs of heaven to be able to investi- 
gate the particular arrangements which enter into 
the physical and moral economy of the celestial 
worlds. Were we transported to the surface of 
the planet Jupiter, and had an opportunity of sur- 
veying, at leisure, the regions of that vast globe, 
and the tribes of sensitive and intellectual existence 
which compose its population — of contemplating the 
relations of its moons to the pleasure and comfort 
of its inhabitants — the constitution of its atmosphere 
as to its reflective and refractive powers, in pro- 
ducing a degree of illumination to compensate for 
the great distance of that planet from the sun — its 
adaptation to the functions of animal life — the con- 
struction of the visual organs of its inhabitants, and 
the degree of sensibility they possess, corresponding 
to the quantity of light received from the sun — the 
temperature of the surface and atmosphere of this 
globe, corresponding to its distance from the central 
source of heat, and to the physical constitution of 
sensitive beings; — in short, could we investigate 
the relations which inanimate nature, in all its 
varieties and sublimities, bears to the necessities 
and the happiness of the animated existences that 
traverse its different regions, w^e should, doubtless, 
behold a scene of divine wisdom and intelligence 
far more admirable and astonishing than even that 
which is exhibited in our sublunary world. But 
since it is impossible for us to investigate the 
economy of other worlds, while we are chained 
down to this terrestrial sphere, we must direct our 
attention to those arrangements and contrivances 
in the constitution of our own globe which lie open 
to our particular inspection, in order to perceive 
more distinctly the benevolent designs of Him " in 
whom we live and move, and have our being." 
And here an attentive observer will find, in almost 
every object, when minutely examined, a display of 
goodness and intelligence which will constrain him 
to exclaim, "0 the depth of the riches both of the 
wisdom and the knowledge of God." 

Wisdom, considered as consisting in contrivance, 
or the selection of the most proper means in order 
to acomplish an important end, may be exemplified 
and illustrated in a variety of familiar objects. 



WONDERS OF THE HEAVENS 



95 



The earth, on which we tread, was evidently in- 
tended by the Creator to support man and other 
animals, along with their habitations, and to furnish 
those vegetable productions which are necessary for 
their subsistence ; and, accordingly, he has given it 
that exact degree of consistency which is requisite 
for these purposes. Were it much harder than it 
now is — were it, for example, as dense as a rock — 
it would be incapable of cultivation, and vegetables 
could not be produced from its surface. Were it 
softer, it would be insufficient to support us, and we 
should sink at every step, like a person walking in 
a quagmire. Had this circumstance not been at- 
tended to in its formation, the earth would have 
been rendered useless as a habitable world for all 
those animated beings which now traverse its sur- 
face. The exact adjustment of the solid parts of 
our globe to the nature and necessities of the beings 
which inhabit it, is, therefore, an instance and an 
evidence of wisdom. 

The diversity of surface which it everywhere pre- 
sents, in the mountains and vales with which it is 
variegated, indicates the same benevolent contri- 
vance and design. If the earth were divested of 
its mountains, and its surface everywhere uniformly 
smooth, there would be no rivers, springs, or foun- 
tains ; for M'^ater can flow only from a higher to a 
lower place ; the vegetable tribes would droop and 
languish ; man and other animals would be deprived 
of what is necessary for their existence and comfort ; 
we should be destitute of many useful stones, 
minerals, plants, and trees, which are now pro- 
duced on the surface and in the interior of moun- 
tains; the sea itself would become a stagnant 
marsh, or overflow the land ; and the whole surface 
of nature in our terrestrial sphere would present 
an unvaried scene of dull uniformity. Those 
picturesque and sublime scenes which fire the 
imagination of the poet, and which render moun- 
tainous districts so pleasing to the philosophic 
traveller, would be completely withdrawn; and all 
around, when compared with such diversified land- 
scapes, would appear as fatiguing to the eye as the 
vast solitudes of the Arabian deserts, or the dull 
monotony of the ocean. But in consequence of 



the admirable distribution of hills and mountains 
over the surface of our globe, a variety of useful 
and ornamental effects is produced. Their lofty 
summits are destined by Providence to arrest the 
vapors which float in the regions of the air; their 
internal cavities form so many spacious basins for 
the reception of waters distilled from the clouds ; 
they are the original sources of springs and rivers, 
that water and fertilize the earth ; they form im- 
mense magazines, in which are deposited stones, 
metals, and minerals, which are of essential ser- 
vice in the arts that promote the comfort of human 
life ; they serve for the production of a vast variety 
of herbs and trees ; they arrest the progress of 
storms and tempests ; they afford shelter and en- 
tertainment to various animals which minister to 
the wants of mankind : in a Avord, they adorn and 
embellish the face of nature, they form thousands 
of sublime and beautiful landscapes, and afford from 
their summits the most delightful prospects of the 
plains below. All these circumstances demonstrate 
the consummate wisdom of the Great Architect of 
nature, and lead us to conclude, that mountains, so 
far from being rude excrescences of nature, as some 
have asserted, form an essential part in the consti- 
tution, not only of our globe, but of all habitable 
worlds. And this conclusion is confirmed, so far 
as our observation extends, with regard to the 
moon, and several of the planetary bodies which 
belong to our system, whose surfaces are found to 
be diversified by sublime ramifications of mountain 
scenery. This circumstance forms one collateral 
proof, among many others, that they are the abodes 
of sentient and intellectual beings. 

Again, the coloring which is spreacl over the face 
of nature indicates the wisdom of the Deity. It is 
essential to the present mode of our existence, and 
it was evidently intended by the Creator, that we 
should be enabled easily to recognise the forms and 
properties of the various objects with which we are 
surrounded. But were the objects of nature desti- 
tute of color, or were the same unvaried hue 
spread over the face of creation, we should be desti- 
tute of all the entertainments of vision, and be at a 
loss to distinguish one object from another. We 



96 



WONDERS OF THE HEAVENS 



should be unable to distinguish rugged precipices 
from fruitful hills ; naked rocks from human habita- 
tions ; the trees from the hills that bear them, and 
the tilled from the untilled lands. "We should 
hesitate to pronounce whether an adjacent inclosure 
contain a piece of pasturage, a plot of arable land, 
or a field of corn; and it would require a little 
journey, and a minute investigation, to determine 
such a point. We could not determine whether 
the first person we met were a soldier in his regi- 
mentals, or a swain in his Sunday suit; a bride in 
her ornaments, or a widow in her weeds." Such 
would have been the aspect of nature, and such the 
inconveniences to which we should have been sub- 
jected, had God allowed us light, without the dis- 
tinction of colors. We could have distinguished 
objects only by intricate trains of reasoning, and by 
circumstances of time, place, and relative position. 
And to what delays and perplexities should we 
have been reduced, had we been obliged every 
moment to distinguish one thing from another by 
reasoning ! Our whole life must then have been 
employed rather in study than in action; and, after 
all, we must have remained in eternal uncertainty 
as to many things, which are now quite obvious to 
every one as soon as he opens his eyes. We could 
neither have communicated our thoughts by writing, 
nor have derived instruction from others through 
the medium of books : so that we should now have 
been almost as ignorant of the transactions of past 
ages as we are of the events which are passing in 
the planetary worlds ; and, consequently, we could 
never have enjoyed a written revelation from hea- 
ven, nor any other infallible guide to direct us in 
the path to happiness, if the Almighty had not dis- 
tinguished the rays of light, and painted the objects 
around us with a diversity of colors : so essentially 
connected are the minutest and the most magnifi- 
cent works of Deity. But now, in the present con- 
stitution of things, color characterizes the class to 
which every individual belongs, and indicates, upon 
the first inspection, its respective quality. Every 
object wears its peculiar livery, and has a distin- 
guishing mark by which it is characterized. 

The different hues which are spread over the 



scenery of the world are also highly ornamental to 
the face of nature, and afford a variety of pleasures 
to the eye and the imagination. It is this circum- 
stance which adds a charm to the fields, the valleys, 
and the hills, the lofty mountain, the winding river, 
and the expansive lake ; and which gives a splendor 
and sublimity to the capacious vault of heaven. 
Color is, therefore, an essential requisite to every 
world inhabited by sensitive beings ; and we know 
that provision has been made for diffusing it through- 
out all the globes which may exist in the distant 
regions which our telescopes have penetrated ; for 
the light which radiates from the most distant stars 
is capable of being separated into the prismatic 
colors, similar to those which are produced by the 
solar rays; which furnishes a presumptive proof 
that they are intended to accomplish designs in 
their respective spheres analogous to those which 
light subserves in our terrestrial habitation ; or, in 
other words, that they are destined to convey to 
the minds of sentient beings impressions of light 
and color, and, consequently, beings susceptible of 
such impressions must reside within the sphere, or 
more immediate influence of these far distant orbs. 
The same benevolent design is apparent in the 
general color which prevails throughout the scene of 
sublunary nature. Had the fields been clothed with 
hues of a deep red or a brilliant white, the eye 
would have been dazzled with the splendor of their 
aspect. Had a dark blue or a black color generally 
prevailed, it would have cast a universal gloom 
over the face of nature. But an agreeable green 
holds the medium between these two extremes, 
equally remote from a dismal gloom and excessive 
splendor, and bears such a relation to the structure 
of the eye that it refreshes instead of tiring it, and 
supports instead of diminishing its force. At the 
same time, though one general color prevails over 
the landscape of the earth, it is diversified by an 
admirable variety of shades, so that every indi- 
vidual object in the vegetable world can be accu- 
rately distinguished from another; thus producing a 
beautiful and variegated appearance over the whole 
scenery of nature. " Who sees not in all these 
things that the hand of the Lord hath wrought this ?" 



WONDERS OF THE HEAVENS. 



97 



If from the earth we turn our attention to the 
waters, we shall perceive similar traces of the 
exquisite wisdom and skill of the Author of nature. 
Water is one of the most essential elementary parts 
in the constitution of our globe, without which the 
various tribes of beings which now people it could 
not exist. It supplies a necessary beverage to man, 
and to all the animals that people the earth and the 
air. It forms a solvent for a great variety of solid 
bodies; it is the element in which an infinitude of 
organized beings pass their existence ; it acts an 
important part in conveying life and nourishment 
to all the tribes of the vegetable kingdom, and gives 
salubrity to the atmospherical regions. Collected 
in immense masses in the basins of the sea, it serves 
as a vehicle for ships, and as a medium of commu- 
nication between people of the most distant lands. 
Carried along with a progressive motion over the 
beds of streams and of rivers, it gives a brisk im- 
pulse to the air, and prevents the unwholesome 
stagnation of vapors ; it receives the filth of popu- 
lous cities, and rids them of- a thousand nuisances. 
By its impulsion it becomes the mover of a multi- 
tude of machines ; and, when rarified into steam, 
it is transformed into one of the most powerful and 
useful agents under the dominion of man. All 
these beneficial effects entirely depend on the 
exact degree of density, or specific gravity, which 
the Creator has given to its constituent parts. 
Had it been much more rarified than it is, it would 
have been altogether unfit to answer the purposes 
now specified ; the whole face of the earth would 
have been a dry and barren waste ; vegetable 
nature could not have been nourished ; our floating 
edifices could not have been supported ; the lightest 
bodies would have sunk, and all regular intercourse 
with distant nations would have been prevented. 
On the other hand, had its parts been much denser 
than they are ; — for example, had they been of the 
consistency of a thin jelly, — similar disastrous ef- 
fects would have inevitably followed ; no ships could 
have ploughed the ocean ; no refreshing beverage 
would have been supplied to the animal tribes ; 
the absorbent vessels of trees, herbs, and flowers 

would have been unable to imbibe the moisture 
13 



requisite for their nourishment ; and we should 
thus have been deprived of all the beneficial effects 
we now derive from the use of that liquid element, 
and of all the diversified scenery of the vegetable 
world. But the configuration and consistency of 
its parts are so nicely adjusted to the constitution 
of the other elements, and to the wants of the sen- 
sitive and vegetable tribes, as exactly to subserve 
the ends intended in the system of nature. 

The most appropriate and impressive illustrations 
of Omnipotence are those which are taken from the 
permanent operations of Deity, which are visible 
every moment in the universe around us ; or, in 
other words, those which are derived from a detail 
of- the facts which have been observed in the 
material world respecting magnitude and motion. 

We must endeavor to form a conception of the 
bulk of the world in which we dwell, which, though 
only a point in comparison of the whole material 
universe, is in reality a most astonishing magnitude, 
which the mind cannot grasp without a laborious 
eflbrt. We can form some definite idea of those 
protuberant masses we denominate hills, which 
arise above the surface of our plains ; but were we 
transported to the mountainous scenery of Switzer- 
land, to the stupendous range of the Andes in 
South America, or to the Himalayan mountains 
in India, where masses of earth and rocks, in every 
variety of shape, extend several hundreds of miles 
in different directions, and rear their projecting 
summits beyond the region of the clouds — we 
should find some difficulty in forming an adequate 
conception of the objects of our contemplation. 
" For," (to use the words of one who had been a 
spectator of such scenes,) " amidst those trackless 
regions of intense silence and solitude, we cannot 
contemplate but with feelings of awe and admira- 
tion the enormous masses of variegated matter 
which lie around, beneath, and above us. The 
mind labors, as it were, to form a definite idea of 
those objects of oppressive grandeur, and feels un- 
able to grasp the august objects which compose 
the surrounding scene." But what are all these 
mountainous masses, however variegated and sub- 
lime, when compared with the bulk of the whole 



98 



WONDERS OF THE HEAVENS 



earth ? Were they hurled from their basis, and 
precipitated into the vast Pacific ocean, they, would 
all disappear in a moment, except perhaps a few 
projecting tops, which, like a number of small 
islands, might be seen rising a few fathoms above 
the surface of the waters. 

In order to form a tolerable conception of the 
whole globe, we must endeavor to take a leisurely 
survey of its different parts. Were we to take our 
station on the top of a mountain, of a moderate size, 
and survey the surrounding landscape, we should 
perceive an extent of view stretching forty miles in 
every direction, forming a circle eighty miles in 
diameter, and two hundred and fifty in circumfer- 
ence, and comprehending an area of five thousand 
square miles. In such a situation the terrestrial 
scene around and beneath us, consisting of hills and 
plains, towns and villages, rivers and lakes, would 
form one of the largest objects which the eye, or 
even the imagination, can steadily grasp at one 
time. But such an object, grand and extensive as 
it is, forms no more than the forty thousandth part 
of the globe; so that, before we can acquire an 
adequate conception of the magnitude of our own 
world, we must conceive forty thousand landscapes 
of a similar extent to pass in review before us : and 
were a scene, of the magnitude now stated, to pass 
before us every hour, till all the diversified scenery 
of the earth were brought under our view, and were 
twelve hours a day allotted for the observation, it 
would require nine years and forty-eight days be- 
fore the whole surface of the globe could be con- 
templated, even in this general and rapid manner. 
But such a variety of successive landscapes passing 
before the eye, even although it were possible to be 
realized, would convey only a very vague and im- 
perfect conception of the scenery of our world ; for 
objects at the distance of forty miles cannot be dis- 
tinctly perceived: the only view which would be 
satisfactory, would be that which is comprehended 
within the range of three or four miles from the 
spectator. 

Again, we have already stated that the surface 
of the earth contains nearly 200,000,000 of square 
miles. Now, were a person to set out on a minute 



survey of the globe, and to travel till he passed 
along every square mile on its surface, and to con- 
tinue his route without intermission, at the rate of 
thirty miles every day, it would require 18,264 years 
before he could finish his tour, and complete the 
survey of " this huge rotundity on which we tread :" 
so that, had he commenced his excursion on the day 
in which Adam was created, and continued it to 
the present hour, he would not have accomplished 
one-third part of this vast tour. 

In estimating the size and extent of the earth, 
we ought also to take into consideration the vast 
variety of objects with which it is diversified, and 
the numerous animated beings with which it is 
stored; — the great divisions of land and water, the 
continents, seas, and islands, into which it is dis- 
tributed ; the lofty ranges of mountains which rear 
their heads to the clouds ; the unfathomed abysses 
of the ocean; its vast subterraneous caverns and 
burning mountains; and the lakes, rivers, and 
stately forests with which it is so magnificently 
adorned ; — the many millions of animals, of every 
size and form, from the elephant to the mite, which 
traverse its surface ; the numerous tribes of fishes, 
from the enormous whale to the diminutive shrimp, 
which "play" in the mighty ocean; the aerial 
tribes which sport in the regions above us, and the 
vast mass of the surrounding atmosphere, which 
incloses the earth and all its inhabitants as " with 
a swaddling band." The immense variety of beings 
with which our terrestrial habitation is furnished, 
conspires, with every other consideration, to exalt 
our conceptions to that Power by which our globe, 
and all that it contains, were brought into exist- 
ence. 

The preceding illustrations, however, exhibit 
the vast extent of the earth considered only as a 
superficies. But we know that the earth is a solid 
globe, whose specific gravity is nearly five times 
denser than water, or about twice as dense as the 
mass of earth and rocks which compose its surface. 
Though we cannot dig into its bowels beyond a 
mile in perpendicular depth, to explore its hidden 
wonders, yet we may easily conceive what a vast 
and indescribable miass of matter must be contained 



WONDERS OF THE HEAVENS 



99 



between the two opposite portions of its external 
circumference, reaching eight thousand miles in 
every direction. The solid contents of this pon- 
derous ball is no less than 263,858,149,120 cubical 
miles — a mass of material substance of which we 
can form but a very faint and imperfect conception 
— in proportion to which all the lofty mountains 
that rise above its surface are less than a few 
grains of sand when compared with the largest 
artificial globe. Were the earth a hollow sphere, 
surrounded merely with an external shell of earth 
and water, ten miles thick, its internal cavity 
would be sufficient to contain a quantity of ma- 
terials one hundred and thirty-three times greater 
than the whole mass of continents, islands, and 
oceans on its surface, and the foundations on which 
they are supported. We have the strongest rea- 



sons, however, to conclude, that the earth, in its 
general structure, is one solid mass, from the sur- 
face to the centre, excepting, perhaps, a few 
caverns scattered here and there amidst its subter- 
raneous recesses: and that its density gradually 
increases from its surface to its central regions. 
What an enormous mass of materials, then, is com- 
prehended within the limits of that globe on which 
we tread ! The mind labors, as it were, to com- 
prehend the mighty idea, and after all its exertion 
feels itself unable to take in such an astonishing 
magnitude at one comprehensive grasp. How great 
must be the power of that Being who commanded 
it to spring from nothing into existence, who 
measureth the ocean in the hollow of his hand, who 
weigheth the mountains in scales and hangeth the 
earth upon nothing. 



CHAPTER III. 



SECTION I. 

Sun — Comparatively stationary — Cause of twilight — ^Sun's mass — 
Gravity — Real diameter — Probable conclusions of the solar astro- 
nomer — Sun's disc as seen from the different planets — Sun the 
source of heat — What proportion of solar light falls on our globe 
— Divine wisdom — Solar spots — Variable in size and number — 
First authentic observations on — Scheiner imagines they are 
planets — Their course and changes — Sun's revolution about its 
axis — Theories of different observers respecting the spots — 
Herschel's theory prevalent — Is the sun inhabited? — Zodiacal 
light — ^Sun's progressive motion— Herschel's theory confirmed by 
a late experiment in France. 

The sun, that might at first be ranked in the num- 
ber of planets or wanderers, has been found to be 
comparatively stationary, and may therefore be re- 
garded as a star, occupying the centre of our sys- 
tem, appearing larger than the rest of the stars only 
on account of its greater proximity to us. 

It appears to us under the form of a round and 
dazzling circle, called its disc. Owing to the 
diurnal motion of the earth, the sun, like the other 
stars, which become invisible in the splendor of his 



light, appears to describe a circle, whose variable 
extent determines the length of the days. His 
descent below the horizon does not instantly plunge 
us into the shades of night; but his luminous rays, 
refracted by the strata of the atmosphere before 
rising and after setting, cause that feeble light 
which we call twilight, and present to our view 
that succession of colors so remarkable for their 
variety of agreeable shades. 

Besides this apparent daily motion of the sun, it 
has another apparent motion in the plane of the 
ecliptic, resulting from the real motion of the earth 
in its annual orbit. It is owing to this motion of 
the earth, which varies the position of the sun in 
respect to an observer, that the latter body appears 
under very diflferent magnitudes, its diameter being 
very sensibly less when in apogee (which happens 
at midsummer) than in perigee, (which happens in 
midwinter;) — a circumstance which is common to 
it with bodies near the surface of our globe. 



100 



WONDERS OF THE HEAVENS 



which appear to us larger in proportion to their 
proximity. 

Calculations give the following results as the 
distance between the sun and the earth at different 
times : — 



Perigee or perihelion 


93,745,237 


Apogee or aphelion 


96,950,457 


Mean distance 


95,347,872 


Longest diameter 


190,695,744 



Thus the greatest distance exceeds the mean by 
about one and a half millions of miles, — a quantity 
very small in comparison with the dimensions of 
the orbit. 

When we calculate from the known distance of 
the sun, and from the period in which the earth 
circulates about it, what must be the centrifugal 
force of the latter, by which the sun's attraction is 
balanced, (and which, therefore, becomes an exact 
measure of the sun's attractive energy as exerted 
on the earth,) we find it to be immensely greater 
than would suffice to counteract the earth's attrac- 
tion on an equal body at that distance — greater in 
the high proportion of 354,936 to 1. It is clear, 
then, that if the earth be retained in its orbit about 
the sun by solar attraction, conformable in its rate 
of diminution with the general law, this force must 
be no less than 354,936 times more intense than 
what the earth would be capable of exerting, other 
things being equal, at an equal distance. 

What, then, are we to understand from this re- 
sult? Simply this, that the sun attracts as a 
collection of 354,936 earths, occupying its place, 
would do, or, in other words, that the sun contains 
354,936 times the mass or quantity of ponderable 
matter that the earth consists of When we com- 
pare its mass with its bulk, we find its density to be 
less than that of the earth, being no more than 
0-2543 ; so that it must consist, in reality, of far 
lighter materials, especially when we consider the 
force under which its central parts must be con- 
densed. This consideration renders it highly 
probable that an intense heat prevails in its in- 
terior, by which its elasticity is reinforced, and 
rendered capable of resisting this almost incon- 
ceivable pressure without collapsing into smaller 
dimensions. 



This will be more distinctly appreciated, if we 
estimate the intensity of gravity at the sun's sur- 
face. 

The attraction of a sphere, being the same as if 
its whole mass were collected in its centre, will, 
of course, be proportional to the mass directly, and 
the square of the distance inversely ; and, in this 
case, the distance is the radius of the sphere. 
Hence we conclude, that the intensities of solar 
and terrestrial gravity at the surfaces of the two 
globes are in the proportions of 27*9 to 1, A 
pound of terrestrial matter at the sun's surface, 
then, would exert a pressure equal to what 27*9 
such pounds would do at the earth's. An ordinary 
man, for example, would not only be unable to 
sustain his own weight on the sun, but would 
literally be crushed to atoms under the load. 

We must then consent to dismiss all idea of the 
earth's immobility, and transfer that attribute to the 
sun, whose ponderous mass is calculated to exhaust 
the feeble attractions of such comparative atoms 
as the earth and moon, without being perceptibly 
dragged from its place. Their centre of gravity 
lies, as we have already hinted, almost close to the 
centre of the solar globe, at an interval quite im- 
perceptible from our distance ; and whether we 
regard the earth's orbit as being performed about 
the one or the other centre makes no appreciable 
difference in any one phenomenon of astronomy. 

That at so vast a distance the sun should appear 
to us of the size it does, and should so powerfully 
influence our condition by its heat and light, re- 
quires us to form a very grand conception of its 
actual magnitude, and of the scale on which those 
important processes are carried on within it, by 
which it is enabled to keep up its liberal and unceas- 
ing supply of these elements. As to its actual mag- 
nitude we can be at no loss, knowing its distance, 
and the angles under which its diameter appears 
to us. An object, placed at the distance of ninety- 
five millions of miles, and subtending an angle of 
32' 3'', must have a real diameter of eight hundred 
and eighty-two thousand miles. Were its central 
parts placed adjacent to the surface of the earth, 
its circumference would reach two hundred thou- 



WONDERS OF THE HEAVENS. 



101 



sand miles beyond the moon's orbit, on every side, 
filling a cubical space of 681,472,000,000,000,000 
miles. If it would require eighteen thousand years 
to traverse every square mile on the earth's sur- 
face, at the rate of thirty miles a day, it would 
require more than two thousand millions of years to 
pass over every part of the sun's surface, at the 
same rate. Even at the rate of ninety miles a day 
it would require more than eighty years to go round 
its circumference. Of a body so vast in its dimen- 
sions, the human mind, with all its efforts, can form 
no adequate conception. It appears an extensive 
universe in itself; and, although no other body 
existed within the range of infinite space, this globe 
alone would afford a powerful demonstration of the 
omnipotence of the Creator. Were the sun a 
hollow sphere, surrounded by an external shell, 
and a luminous atmosphere; were this shell per- 
forated with several hundreds of openings into the 
internal part ; were a globe as large as the earth 
placed at its centre, and another globe as large as 
the moon, and at the same distance from the centre 
as the moon is from us, to revolve round the cen- 
tral globe, — it would present to the view a uni- 
verse as splendid and glorious as that which now 
appears to the vulgar eye, — a universe as large 
and extensive as the whole creation was conceived 
to be by our ancestors, in the infancy of astro- 
nomy. 

It is hardly possible to avoid associating our 
conception of an object of definite globular figure, 
and of such enormous dimensions, with some cor- 
responding attribute of massiveness and material 
solidity. That the sun is not a mere phantom, but 
a body having its own peculiar structure and 
economy, our telescopes distinctly inform us. They 
show us dark spots on its surface, which slowly 
change their places and forms, and by attending 
to their situation, at different times, astronomers 
have ascertained that the sun revolves about an 
axis inclined at a constant angle of 82° 40' to 
the plane of the ecliptic, performing one rotation 
in a period of twenty-five days, and in the same 
direction with the diurnal rotation of the earth, i. e. 
from west to east. Here, then, we have an ana- 



logy with our own globe ; the slower and more 
majestic movement only corresponding with the 
greater dimensions of the machinery, and impress- 
ing us with the prevalence of similar mechanical 
laws, and of, at least, such a community of nature 
as the existence of inertia and obedience to force 
may argue. Now, in the exact proportion in which 
we invest our idea of this immense bulk with the 
attribute of inertia, or weight, it becomes difficult 
to conceive its circulation round so comparatively 
small a body as the earth, without, on the one 
hand, dragging it along, and displacing it, if bound 
to it by some invisible tie ; or, on the other hand, 
if not so held to it, pursuing its course alone in 
space, and leaving the earth behind. If we tie 
two stones together by a string, and fling them 
aloft, we see them circulate about a point between 
them, which is their common centre of gravity ; 
but if one of them be greatly more ponderous than 
the other, this common centre will be proportion- 
ally nearer to that one, and even within its surface, 
so that the smaller one will circulate, in fact, about 
the larger, which will be comparatively but little 
disturbed from its place. The sun being at the 
centre of all the planets' motions, the only place 
from which these motions would appear such as 
they actually are would be the centre of that 
luminary. 

There, the observer, not being supposed to turn 
round with the sun's rotation, would see all the 
stars at rest and seemingly equidistant from him. 
The planets would appear to move among the fixed 
stars in a simple, regular and uniform manner, 
only they would not describe equal portions of 
their orbits in equal times. They would appear 
to move from west to east in the heavens, in paths 
that cross at small angles, and then separate a 
little from each other. So that if the solar astrono- 
mer should take the orbit of any one planet as his 
standard, and consider it as having no obliquity, 
he would judge the paths of all the rest to be in- 
clined to this standard, each planet having one 
half its path on one side and the other half on the 
opposite side of the standard. 

Suppose now he should see all the planets start 



102 



WONDERS OF THE HEAVENS 



from the same line, crossing the standard orbit at 
right angles. Mercury would move so much faster 
than Venus as to go wholly round his orbit and 
again overtake her in the space of one hundred and 
forty-five of our days ; Venus so much faster than 
the Earth as to overtake it again in five hundred 
and eighty-five days ; the Earth so much faster 
than Mars as to overtake him again in seven hun- 
dred and seventy-eight days. 

But as the solar astronomer would have no idea 
of measuring by our days, he might perhaps take 
the period of Mercury's revolution, being the most 
rapid in its motions, as a measure, with which to 
estimate the periods of the rest. As all the stars 
would appear without motion, he would not think 
that they had any dependence on the sun ; but 
would naturally conclude that the planets have, 
because they move round the sun ; and perhaps 
he might suppose that those planets whose periods 
were shortest, moved in orbits proportionably less 
than those whose periods were longer. But as to 
him they would have no parallax, he could not 
know their real distances or magnitudes. Their 
relative distances he misht guess at from their 
periods, aad thence infer something of their rela- 
tive sizes, by comparing their apparent sizes with 
one another. For example, Jupiter appearing 
larger than Mars, he would conclude it much 
larger, as he had from its period concluded that it 
was much more distant. Mercury and the Earth 
would appear nearly of the same size ; but having 
concluded, from the Earth's longer period, that it 
was farther off than Mercury, he would conclude 
that our globe was really larger. And as each 
planet would appear sometimes larger than at 
others, and to move most rapidly when it seem- 
ed largest, he could determine that all the planets 
moved in orbits of which the sun is not exactly at 
the centre. 

As the planets are at very different distances 
from the sun, the apparent disc of that luminary 
will vary in magnitude at the ^different planets. 
Suppose No. 1 to represent the size of the disc as 
seen from Mercury ; then at Venus it will appear 
a little more than one half as large, and may be 



represented by No. 2. No. 3 will be the apparent 
disc at the Earth ; No. 4 at Mars ; No. 5 at 




Jupiter ; No. 6 at Saturn. At Herschel it would 
be represented by a circle one half as large as 
No. 6 ; Herschel being twice as far from the sun 
as Saturn. 

The sun is the grand source of light and heat, 
both to the earth and to all the other planetary 
bodies. The heat he diffuses animates every part 
of our sublunary system, and all that variety of 
coloring which adorns the terrestrial landscape is 
produced by his rays. It has been lately discover- 
ed, that the rays of light, and the rays of heat, or 
caloric, are distinct from each other; for, it can be 
demonstrated, that some rays from the sun produce 
heat, which have no power of communicating light 
or color. The greatest heat is found in the red 
rays, the least in the violet rays ; and in a space 
beyond the red rays, where there is no light, the 
temperature is greatest. The rays of the sun have 
also been found to produce different chemical ef- 
fects. The white muriate of silver is blackened in 
the violet ray, in the space of fifteen seconds, 
though the red will not produce the same effect in 
less than twenty minutes. Phosphorus is kindled 
in the vicinity of the red ray, and extinguished in 
the vicinity of the violet. The solar light, there- 
fore, consists of three different orders of rays, one 
producing color, a second producing heat, and a 
third chemical effects. Euler has computed that 
the light of the sun is equal to six thousand five 
hundred candles at a foot distance, while the 
moon would be as one candle at seven and a half 
feet ; Venus at four hundred and twenty-one feet ; 
and Jupiter at one thousand three hundred and 
twenty feet. That this immense luminary appears 
so small to our eyes is owing to its vast distance, 



WONDERS OF THE HEAVENS 



103 



which is no less than ninety-five millions of miles. 
Some faint idea of this distance may be obtained, 
by considering, that a steam-boat, moving at the 
rate of two hundred miles a day, would require 
thirteen hundred years before it could traverse the 
space which intervenes between us and the sun. 

From a consideration of the rays of light, we are 
led to investigate what proportion of the solar light 
falls upon our globe, in order to produce so diversi- 
fied a scene of sublimity and beauty. Supposing 
the sun's rays to be chiefly confined, in their ef- 
fects, within the limits of the planetary system, 
since they diverge in every direction, they must 
fill a cubical space 3,600,000,000 miles in dia- 
meter; which, consequently, will contain about 
24,000,000,000,000,000,000,000,000,000 of cubi- 
cal miles ; so that an eye, placed in any point of this 
vast space, would receive a distinct impression 
from the solar rays. The solidity of the earth is 
about 264,000,000,000 cubical miles, and, there- 
fore, it receives only the 9o.oo» - ,ooo,ooo,ooo ;CTTyTTth part 
of the light which fills the sphere of the solar 
system. So that the light which cheers all the 
inhabitants of the world, and unveils such a variety 
of beautiful and magnificent objects, is nothing 
more than a single stream of celestial radiance out 
of ninety thousand billions of similar streams, 
which the great source of light is every moment 
diifusing throughout the surrounding worlds. But 
the solar rays are not confined within the bounds 
of the planetary system ; their influence extends, 
in every direction, as far as the nearest stars, filling 
a cubical space at least 40,000,000,000,000 miles 
in diameter, and which contains 33,500,000,000,- 
000,000,000,000,000,000,000,000,000,000, or thir- 
ty-three thousand five hundred sextillions of cubi- 
cal miles. And, were we to institute comparisons 
and calculations, with respect to the possible 
variety of effects they might produce throughout 
this immense region, whole pages might be filled 
with figures, cyphers, and computations. We might 
compute how many globes similar to the earth, or 
any of the larger planets, might be contained with- 
in this vast space, allowing several hundreds of 
cubical miles of empty space around each globe — 



how many myriads of refractions and reflections 
the rays of light would suffer, in regard to the 
peculiar objects connected with every one of these 
globes — how many eyes of sentient beings might 
be affected by the diversities of color, shape, and 
motion which would thus be produced — and what 
a variety of shades of light and color, and what a 
diversity of scenery, would be produced, according 
to the distance of the respective globes from the 
central luminary. The planetary system — that 
portion of the heavens with which we are best 
acquainted — displays both the magnificence and 
the skill of its Divine Author, — in the magnitudes, 
distances, revolutions, proportions, and uses of the 
various globes of which it is composed, and in the 
diversified apparatus by which light and darkness 
are alternately distributed. The sun, an immense 
luminous world, by far the largest body in the 
system, is placed in the centre. No other position 
would have suited for an equable distribution of 
illumination and heat through the different parts of 
the system. Around him, at different distances, 
eleven primary planets revolve, accompanied with 
eighteen secondaries, or moons, — all in majestic 
order and harmony, no one interrupting the move- 
ments of another, but invariably keeping the paths 
prescribed them, and performing their revolutions 
in their appointed times. To all these revolving 
globes, the sun dispenses motion, light, heat, fer- 
tility, and other unceasing energies, for the comfort 
and happiness of their respective inhabitants ; 
without which, perpetual sterility, eternal winter, 
and eternal night, would reign over every region 
of our globe, and throughout surrounding worlds. 

The distance at which the heavenly bodies, par- 
ticularly the sun, are placed from the earth, is a 
manifest evidence of divine wisdom. If the sun 
were much nearer us than he is at present, the 
earth, as now constituted, would be wasted and 
parched with excessive heat ; the waters would be 
turned into vapor, and the rivers, seas, and oceans, 
would soon disappear, leaving nothing behind them 
but frightful barren dells and gloomy caverns ; 
vegetation would completely cease, and the tribes 
of animated nature languish and die. On the other 



104 



WONDERS OF THE HEAVENS. 



hand, were the sun much farther distant than he 
now is, or were his bulk, or the influence of his 
rays, diminished one half of what they now are, 
the land and the ocean would soon become one 
frozen mass, and universal desolation and sterility 
would overspread the fair face of nature, and, 
instead of a pleasant and comfortable abode, our 
globe would become a frightful desert, a state of 
misery and perpetual punishment.* 

When viewed through powerful telescopes, pro- 
vided with colored glasses, to take off the heat, 
which would otherwise injure our eyes, the sun is 
observed to have frequently large and perfectly 
black spots upon it, surrounded with a kind of 
border, less completely dark, called a penumbra. 
Some of these are represented in this figure. 




Occasionally they break up, or divide into two or 
more, and in those offer every evidence of that 
extreme mobility which belongs only to the fluid 
state, and of that excessively violent agitation 
which seems only compatible with the atmospheric 
or gaseous state of matter. The scale on which 
their movements take place is immense. A single 
second of angular measure, as seen from the earth, 
corresponds on the sun's disc to four hundred and 
sixty-five miles ; and a circle of this diameter (con- 
taining therefore nearly two hundred and twenty 

* It forms no objection to these remarks, that caloric, or the matter 
of Aeai, does not altogether depend upon the direct influence of the 
solar rays. The substance of caloric may be chiefly connected with 
the constitution of the globe we inhabit. But still, it is quite certain, 
that the earth, as presently constituted^ would suffer effects most dis- 
astrous to sentient beings, were it removed much nearer or much far- 
ther from the central luminary. 



thousand square miles) is the least space which 
can be distinctly discerned on the sun as a visible 
area. 

The part of the sun's disc not occupied by spots 
is far from uniformly bright. Its ground is finely 
mottled with an appearance of minute dark dots, 
or pores, which, when attentively watched, are 
found to be in a constant state of change. There 
is nothing which represents so faithfully this ap- 
pearance as the slow subsidence of some flocculent 
chemical precipitates in a transparent fluid, when 
viewed perpendicularly from above : so faithfully, 
indeed, that it is hardly possible not to be impress- 
ed with the idea of a luminous medium intermixed, 
but not confounded, with a transparent and non- 
luminous atmosphere, either floating as clouds in 
our air, or pervading it in vast sheets and columns 
like flame, or the streamers of our northern lights. 

It has been noticed, (not without great need of 
further confirmation,) that extinct spots have again 
broken out, after long intervals of time, on the 
same identical points of the sun's globe. Our 
knowledge of the period of its rotation (which, ac- 
cording to Delambre's calculations, is 25-01154 d., 
but, according to others, materially different,) can 
hardly be regarded as sufficiently precise to estab- 
lish a point of so much nicety. 

That the temperature at the visible surface of 
the sun cannot be otherwise than very elevated, 
much more so than any artificial heat produced in 
our furnaces, or by chemical or galvanic processes, 
we have indications of several distinct kinds: 1st, 
From the law of decrease of radiant heat and light, 
which being inversely as the squares of the dis- 
tances, it follows, that the heat received on a given 
area exposed at the distance of the earth, and on 
an equal area at the visible surface of the sun, must 
be in the proportion of the area of the sky occupied 
by the sun's apparent disc to the whole hemi- 
sphere, or as one to about three hundred thousand. 
A far less intensity of solar radiation, collected in 
the focus of a burning-glass, suflSces to dissipate 
gold and platina in vapor. 2dly, From the facility 
with which the calorific rays of the sun traverse 
glasS) a property which is found to belong to the 



WONDERS OF THE HEAVENS. 



105 



heat of artificial fires in the direct proportion of 
their intensity. 3dly, From the fact, that the most 
vivid flames disappear, and the most intensely 
ignited solids appear only as black spots on the 
disc of the sun when held between it and the eye. 
From this last remark it follows, that the body of 
the sun, however dark it may appear when seen 
through its spots, may, nevertheless, be in a state 
of most intense ignition. It does not, however, 
follow of necessity that it must be so. 

The sun's rays are the ultimate source of almost 
every motion which takes place on the surface of 
the earth. By its heat are produced all winds, and 
those disturbances in the electric equilibrium of the 
atmosphere which give rise to the phenomena of 
terrestrial magnetism. By their vivifying action 
vegetables are elaborated from inorganic matter, 
and become, in their turn, the support of animals 
and of man, and the sources of those great de- 
posites of dynamical efficiency which are laid up 
for human use in our coal strata. By them the 
waters of the sea are made to circulate in vapor 
through the air, and irrigate the land, producing 
springs and rivers. By them are produced all dis- 
turbances of the chemical equilibrium of the ele- 
ments of nature, which, by a series of compositions 
and decompositions, give rise to new products, and 
originate a transfer of materials. Even the slow 
degradation of the solid constituents of the surface, 
in which its chief geological changes consist, and 
their diffiision among the waters of the ocean, are 
entirely due to the abrasion of the wind and rain, 
and the alternate action of the seasons ; and when 
we consider the immense transfer of matter so pro- 
duced, the increase of pressure over large spaces 
in the bed of the ocean, and diminution over cor- 
responding portions of the land, we are not at a 
loss to perceive how the elastic power of subterra- 
nean fires, thus repressed on the one hand, and 
relieved on the other, may break forth in points 
where the resistance is barely adequate to their re- 
tention, and thus bring the phenomena of even 
volcanic activity under the general law of solar 
influence. 

The great mystery, however, is to conceive how 
14 



so enormous a conflagration (if such it be) can be 
kept up. Every discovery in chemical science 
here leaves us completely at a loss, or, rather, 
seems to remove farther the prospect of probable 
explanation. If conjecture might be hazarded, we 
should look rather to the known possibility of an 
indefinite generation of heat by friction, or to its 
excitement by the electric discharge, than to any 
actual combustion of ponderable fuel, whether solid 
or gaseous, for the origin of the solar radiation. 
The spots are very variable in their number, their 
form, and their position. Sometimes they suddenly 
disappear, and their places are supplied by others ; 
sometimes there can be counted fifty or more, and 
yet the succeeding year there may be none dis- 
coverable. 

Some of the spots are as large as would cover 
the whole continent ; others have been observed 
of the size of the whole surface of the earth ; and 
one was seen in 1779 which was computed to be 
more than fifty thousand miles in diameter. But 
from certain accounts we have reason to believe 
that there have been spots observed much larger 
even than that, or rather that the sun was all spot ; 
for it is related that, about the year 535, the light 
of the sun was dimmed for the space of fourteen 
months, and that, in the year 626, half the disc 
was obscured during the whole summer. 

We now proceed to give a more full account of 
the spots, as they have been observed by various 
astronomers, and the theories to which they have 
given rise ; considering them all as opinions merely, 
which future discoveries may establish or over- 
throw. Though these spots have sometimes been 
sufficiently large to be distinguished by the naked 
eye, yet they were not discovered till after the in- 
vention of the telescope. They appear to have 
been first seen by Harriot, to whom the science of 
algebra was under great obligations, or by John 
Fabricius, who published an account of his observa- 
tions in 1611 at Wittemberg. The observations 
of Harriot upon the solar spots began on the 8th of 
December, 1610. It is obvious, indeed, from the 
work of Fabricius, that he had seen the sun's spots 
during the year 1610, but it is not certain that he 



106 



WONDERS OF THE HEAVENS. 



saw them before Harriot. It is a remarkable cir- 
cumstance that Fabricius was acquainted with no 
method of intercepting the sun's rays in order to 
save the eye. He observed the sun when he was 
in the horizon, and when his brilliancy was im- 
paired by thin clouds and floating vapors: and he 
advises those who repeat his observations to re- 
ceive at first a small portion of the sun, and gradu- 
ally accustom the eye to a greater portion, till 
it is able to bear the full blaze of its light. When 
the altitude of the sun became considerable, 
Fabricius was compelled to abandon his observa- 
tions. 

At the beginning of the year 1611, Scheiner and 
Galileo seem to have observed, about the same 
time, the spots of the sun. Scheiner was professor 
of mathematics at Ingolstadt : and having accident- 
ally turned his telescope to the sun when thin clouds 
were flying across his disc, he perceived a number 
of black spots, and showed them to several of his 
pupils. The report of this discovery was widely 
propagated, and though Scheiner was solicited by 
many of his friends to publish an account of the 
solar spots, yet he Avas prevented from yielding to 
their wishes by a dread of the ecclesiastical power. 
Scheiner imagined that the spots which appeared 
on the sun did not belong to that luminary, but 
were planets, like Mercury and Venus, which re- 
volved in orbits not very distant from the sun. 
Galileo, who had already made many observations 
on the solar spots, and to whom Velser transmitted 
a copy of Scheiner's letters, with the request that 
he would favor him with his opinion of the new 
phenomena, was at first averse to hazard his senti- 
ments on a subject which might again provoke the 
hostility of the church ; but on the 4th of May, 1612, 
he at length ventured to express his opinions to 
Velser, and to combat the notion entertained by 
Scheiner of the cause of the solar spots. Galileo 
observed that these spots were not of a permanent 
form, as they ought to have been if they were satel- 
lites, but that they often united, separated, in- 
creased and dispersed, like vapors or clouds. He 
maintains that these spots are upon the surface of 
the sun ; that they describe circles parallel to each 



other; that the motion of the sun around its axis 
every month again presents the spots to our view ; 
that some of the spots continue one or two days, 
and others thirty or forty; that they contract in 
their breadth, w^hen they approach the sun's limb, 
without suflfering any diminution of their length ; 
and that they are seldom seen at a greater distance 
than thirty degrees from the sun's equator. Galileo 
likewise perceived on the disc of the sun faculae or 
luculi, which are spots brighter than the rest of his 
disc, and which move in the same manner as the 
dark spots. 

The spots of the sun have been distinctly ob- 
served since the time of Galileo, and many new 
and curious facts have been brought to light respect- 
ing these interesting phenomena. The spots are 
very various, both in magnitude and shape. Most 
of them have a very dark nucleus, surrounded by 
an umbra or a fainter shade. The boundary be- 
tween the umbra and the nucleus is distinct and 
well defined, and the part of the umbra nearest the 
dark nucleus is generally brighter than the more 
distant portion. However irregular be the outline 
of the dark nucleus, the outer circumference of the 
umbra is always curvilineal, without any angles or 
sharp projections. When any spot begins to in- 
crease or diminish, the nucleus and umbra expand 
and contract at the same time. During the process 
of diminution, the umbra encroaches gradually upon 
the nucleus; so that the figure of the nucleus, and 
the boundary between it and the umbra, are in a 
state of perpetual change ; and it often happens 
that, during these variations, the encroachment of 
the umbra divides the nucleus into two or more 
nuclei. When the spots disappear the umbra 
continues for a short time visible after the nucleus 
has vanished, and unless the umbra is succeeded by 
a facula, or luminous spot, the place where it disap- 
pears resembles the other portions of the solar sur- 
face. Large umbrae are seldom seen without a 
nucleus in their centre, but small umbras frequently 
appear by themselves. When Dr. Long was 
examining the sun's image, received upon a sheet 
of white paper, he observed a large round spot 
divide itself into two spots, which receded from each 



WONDERS OF THE HEAVENS 



107 



other with immense rapidity. Dr. Wollaston per- 
ceived a phenomenon of a similar kind Avith a 
twelve inch reflector. A spot burst in pieces when 
he was observing it, like a piece of ice, which, 
thrown upon a frozen pond, breaks in pieces and 
slides in various directions. 

Besides these changes in the spots, which are 
owing to some cause with which we are yet unac- 
quainted, they undergo variations of an optical kind, 
from their change of position on the disc of the sun. 
The nature of this variation will be easily under- 
stood by placing a black spot upon a common 
globe, and observing the different shapes which it 
assumes while the globe is made to revolve about 
its axis. When the spot is near the middle of the 
sun's disc, its breadth is then greater, but it 
diminishes gradually as it advances towards the 
edge of his disc. This variation in the figure of 
the spots, and some of the other variations already 
mentioned, are represented in the annexed plate. 



1 vm^wf \ -^^ 







"' -f,5 



where are given the appearances of a spot on 
seven successive days, as observed by Helve- 
lius. Hence it is obvious th^t these spots are 
upon the surface of the sun, and that their 
motion across his disc from east to west is pro- 
duced by the revolution of the sun about his 
axis. The time in which any spot returns to its 
former position upon the sun's disc is about twenty- 
seven days seven hours and thirty-seven minutes : 
but as the earth has, during this time, advanced in 
its orbit from east to west, and in some measure 
followed the motion of the spot, the real time in 
which the spots perform their revolution will be 
found to be twenty-five days and ten hours. This 



will be understood by supposing that a spot has 
just vanished behind the western limb of the sun: 
in the course of twenty-seven days seven hours and 
thirty-seven minutes it again vanishes behind the 
same limb; but during this interval of time the 
earth has advanced in its orbit, and in the same 
direction with the spot : and therefore, when the 
spot reaches the sun's western limb, after one com- 
plete revolution, the western limb of the sun, be- 
hind which it vanishes, has shifted in absolute space 
to the westward, so that the spot has performed a 
complete revolution and part of a revolution around 
the centre of the sun. We have therefore 365 d. 
5h. 48' + 27d. 7h. 37', or 392d. 13h. 25' is to 
365d. 5h. 48' as 27d. 7h. 37', the apparent revo- 
lution of the spots, is to 25d. 9h. 56', the real 
revolution of the spot, or the time in which the sun 
performs its rotation about its axis. The axis of 
the sun, around which this revolution is performed, 
is inclined 7° 20' to the ecliptic, and the node of 
the solar equator is in the 18th degree of the Twins. 
The solar spots are never seen towards the poles 
of that luminary. They are generally confined 
within a zone stretching about 30° 5' on both sides 
of his equator, though sometimes they have been 
seen in the latitude of 39° 5'. 

Silberschlay, of Magdeburgh, made several ob- 
servations on the solar spots in the year 1768, 
from which he draws the strange conclusions, that 
they have a motion of rotation, and that they 
change their place on the surface of the sun, inde- 
pendent of his monthly revolution. He also con- 
cluded that the spots had not merely the dimensions 
of length and breadth, but that they consisted of 
thick masses of opaque matter. 

Galileo, Hevelius and Maupertuis seem to have 
considered the spots as scoria (dross) floating in the 
inflammable liquid matter of which they conceive 
the sun to be composed. This opinion, however, 
will appear highly improbable, when we consider 
the regularity whh which the spots frequently re- 
appear on the eastern limb of the sun, and the 
effect that the centrifugal force of the sun would 
have in carrying all this floating dross to the equa- 
torial regions. 



108 



WONDERS OF THE HEAVENS. 



De la Hire and La Lande considered the solar spots 
as arising from the opaque body of the sun, the 
eminences of which are sometimes uncovered, in 
consequence of the alternate flux and reflux of the 
liquid igneous matter in which that opaque mass is 
generally enveloped. The part of the opaque 
mass which thus rises above the general surface 
gives the appearance of the nucleus, while those 
parts of the opaque mass which lie only a little 
beneath the igneous matter produce the appear- 
ance of the surrounding umbra. 

This theory was very ably opposed by Dr. 
Wilson, professor of practical astronomy in the 
university of Glasgow, who maintained, with great 
appearance of truth, that the solar spots are de- 
pressions rather than elevations, and that the black 
nucleus of every spot is the opaque body of the sun, 
seen through an opening in the luminous atmos- 
phere with which he is encircled. This explana- 
tion was suggested to Wilson by the phenomena of 
the great solar spot which appeared in November 
1769, and is founded on the following facts: — when 
any spot is about to disappear behind the sun's 
western limb, the eastern portion of the umbra first 
contracts in its breadth, and then vanishes. The 
nucleus then gradually contracts and vanishes, 
while the western portion of the umbra still remains 
visible. When a spot comes into view on the sun's 
eastern limb, the eastern portion of the umbra first 
becomes visible, then the dark nucleus, and then 
the western part of the umbra makes its appear- 
ance. When two spots are near each other, the 
umbra of the one spot is deficient on the side next 
the other; and when one of the spots is much 
larger than the other, the umbra of the largest 
will be completely wanting on the side next the 
smaller. If the large spot have little ones on 
each side of it, its umbra does not totally vanish, 
but seems flattened and pressed in towards the 
nucleus: but the umbra again expands from this 
compressed state as soon as the little spots disap- 
pear. From this cause Wilson concluded, that the 
western portion of the umbra may disappear before 
the nucleus, when a small spot happens to appear 
on the western side of the nucleus. All these ap- 



pearances strongly confirmed the opinion of Wilson, 
that the black part of the spots is the dark body of 
the sun, seen through an opening in the luminous 
matter. 

Dr. Wollaston and La Lande, however, main- 
tained, that though the umbra generally varies 
according to the manner now described, yet the 
phenomenon is not universal, and cannot therefore 
be employed as the foundation of a system. La 
Lande mentions three observations of his own, and 
four observations by Cassini and De la Hire, in 
which the umbra did not vanish, as Dr. Wilson de- 
scribes it. This anomaly, however, may have 
arisen from some small spots in the neighborhood 
of the large one, and cannot possibly be considered 
as an argument that the spots are not excavations 
in the sun's surface. At all events, it may be shown 
that in some spots the umbra may not change as it 
approaches the limb, in consequence of the shallow- 
ness and gradual shelving of the opening in the 
luminous atmosphere. 

In order to confirm experimentally his theory of 
the solar spots. Dr. Wilson constructed a globe, 
consisting of two strong hollow hemispheres, form- 
ed by pasting slips of paper upon a wooden ball, 
and afterwards fastened together upon an iron axis. 
A thick paste, made of glue and Spanish white, 
was laid, in successive coats, upon this outward 
shell, till it became of considerable thickness. The 
globe was then made smooth and spherical ; and as 
soon as it was dried, and the crust white, the spots 
or excavations Avere made in its surface, by boring 
instruments of steel, constructed, in all their cutting 
edges, from a scale of parts of the diameter of the 
ball. The bottom of the hollows were then painted 
black with India ink, and the slope, or shelving 
sides of the excavations, were distinguished from 
the brightness of the external surface by a shade of 
the pencil, which increased toward the external 
border. When this artificial sun was fixed in a 
suitable frame, and examined, at a great distance, 
with a telescope, the umbra and the nucleus ex- 
hibited the same phenomena which have been ob- 
served in the real sun. 

La Lande objected to Dr. Wilson's theory, that 



WONDERS OF THE HEAVENS. 



109 



the great spots seen by De la Hire on the 3d 
of June 1703, and by Cassini in 1719, made an 
indentation or notch in the solar disc, which he 
conceived to be incompatible with the opinion that 
this spot was an excavation. Wilson, however, 
showed, that excavations may cause something like 
an indentation in the sun's limb; and maintained 
that the notches did not always accompany large 
spots ; and that the infrequency of their occurrence, 
and the want of accurate observations, should pre- 
clude astronomers from bringing them forward in 
support of any class of opinions. 

We conceive that the most irrefragable objection 
to the opinion that the spots are eminences which 
rise above the general level of the luminous matter, 
arises from the uniform diminution of the spots as 
they advance from the central part of the sun to his 
western limb. If these dark solar mountains are 
deserted by the luminous matter, why do they ap- 
pear largest when they reach the centre of the 
sun's disc ? Whenever the height of the moun- 
tains greatly exceeds the diameter of their base, 
instead of contracting in the dimension of breadth, 
they ought to increase as they approach the limb ; 
and, at all events, should exhibit phenomena very 
different from what should take place upon the 
supposition that the spots are depressions in the 
luminous matter. It may be said, indeed, that the 
height of these eminences bears no proportion to 
the diameter of their base; but this is an assump- 
tion of which no theorist is entitled to avail himself. 

The faculse, or parts of the surface of the sun 
which are brighter than the rest of his disc, require 
to be examined with good telescopes. They are 
generally seen in the places where spots have ap- 
peared : and sometimes the facula which envelopes 
an assemblage of spots is distinguished by a very 
great degree of brilliancy. These bright spots, 
according to Wollaston, are often converted into 
dark ones. He observed a bright spot appear on 
the east limb of the sun, which next day became a 
dark spot. He also observed a mottled appearance 
over the face of the sun, which, though most visible 
near the limb, was also perceptible in the centre, 
but never appeared towards the poles. The cele- 



brated astronomer Messier made a number of 
curious observations upon the solar faculae. He 
often saw them enter upon the disc of the sun, dis- 
appear as they approached the centre, and after- 
wards reappear on his other limb. In general they 
continued visible for about three days after they 
appeared, and were seen for the same space of time 
before they quitted the sun's western limb. In 
these faculae, spots generally arise of a magnitude 
proportioned to the brightness of the faculae. When 
this did not happen. Messier found that the faculae 
were the precursors of spots, which ordinarily ap- 
peared near the same place on the following day ; 
and hence he was always able to predict the ap- 
pearance of spots about twenty-four hours before 
they entered the sun's disc, and to anticipate, from 
the situation and brightness of the faculae, the 
brilliancy and position of the spots themselves. 
Schroeter saw these faculae in every part of the 
sun's limb, but particularly in a zone between 
twenty degrees of north and twenty degrees of 
south latitude. They generally subtended an an- 
gle of about two or three minutes, and always 
appeared most brilliant when they were near the 
limb. 

Such are the observations which were made on 
the solar spots before they were examined by the 
powerful telescope of Dr. Herschel. This astrono- 
mer continued his observations from 1779 to 1794, 
and has disclosed a number of curious phenomena, 
which throw much light upon the nature and con- 
struction of the sun. Before we direct the atten- 
tion of the reader to the several conclusions which 
he has deduced, we shall give an account of the 
different phenomena which he observed on the 
surface of that luminary. It will be necessary, 
however, to premise, that he regarded the luminous 
surface of the sun as neither a liquid substance nor 
an elastic fluid, but as luminous clouds floating in 
the solar atmosphere ; and that he considered the 
dark nucleus of the spots as the opaque body of the 
sun, appearing through the openings of his atmos- 
phere. Rejecting the old terms of spots, nuclei, 
umbrae, faculae, &.c. Dr. Herschel framed a new 
nomenclature, and comprehended all the solar ap- 



110 



WONDERS OF THE HEAVENS 



pearances under the names of openings, shallows, 
ridges, nodules, corrugations, indentations, and 
pores. 

Openings are those appearances in which the 
opaque body of the sun is visible, in consequence 
of the removal of part of the luminous clouds. 
One of these openings, with a shallow about it, which 
was seen on the 4th of January 1801, a good way 
past the sun's centre, is represented in the plate. 

J ^? 



^1 



On the western side of the shallow, its thickness 
was visible from its surface downwards ; but on the 
eastern side its thickness could not be seen, the 
edge of the shallow only being visible. A section 
of this opening is shown in the figure, where the 



TIF- 



#.t 



k 



I Mi 

e £ , ! 

E I ■ a 

I \ \ \ 

%. i I i i 
\ : i i i 

}^ 






lines abcdef, corresponding with those in the last 
figure, are supposed to be drawn from the eye of 
the observer. The line d passes through the 
opening to the opaque body of the sun. It is 
obvious that the thickness of the shallow is 
visible only on one side, from the position of the 
observer's eye. Large openings are generally- 



surrounded with shallows, though many openings, 
and particularly small ones, have no shallows. 
Openings have a tendency to run into each other, 
and new ones often break out near others. Ridges 
and nodules generally accompany openings. Dr. 
Herschel imagined that the openings are produced 
by an elastic gas, which issues through the incipient 
openings or pores, and, forcing its way through 
them, spreads itself on the luminous clouds. The 
direction of the gaseous stream is often oblique; 
so that the luminous clouds are drawn laterally, 
and form a larger shallow on one side. Openings 
sometimes have a difference of color. They divide 
when decayed, and sometimes they increase again, 
but in general, when they are divided, they diminish 
and disappear, leaving the surface more than usually 
disturbed. They are sometimes converted into 
large indentations, and not unfrequently into pores. 




M 



Fig. 1 represents an opening, with a branch from 
its shallow. In the course of an hour it assumed 
the appearance shown in fig. 2. Fig. 3 is another 
opening with a long shallow. In three hours it 
assumed the appearance of fig. 4; and an hour 
after this an opening appeared in the shallow, as in 
fig. 5. The openings are generally at their greatest 
extent, as in fig. 6, when the shallows begin to 
vanish and the lips or projections to disappear. 
The division of the decaying opening is shown in 
fig. 7, where the luminous passage across the open- 
ing resembles a bridge thrown over a hollow. 

Shallows are places from which the luminous 
solar clouds of the upper regions are removed, and 
are therefore depressed below the general level of 
the surface of the sun. The thickness of the shal- 
lows is visible. They sometimes exist without 
openings. They generally begin from the open- 



WONDERS OF THE HEAVENS 



111 



ings, or branch out from the shallows already form- 
ed, and go forwards. Fig. 8 shows the two 
branches, A B, of a shallow proceeding from an 
opening, C. In the course of half an hour, the 
shallow B is nearly united to the narrow part of 
the shallow surrounding the opening D, while the 



8. 



E 



9- Sm 



i B 



10. 



F 1 :■ B '"i#'" 



f 






*S^ 



■'"'c 



D 






shallow A seems to advance in a direction towards 
the opening E. In the space of another half hour, 
the shallow B (fig. 9) has completely run into 
the shallow about D, while the shallow A has in- 
creased in breadth towards F. The shallow be- 
came afterwards pointed, as in fig. 10, and in the 
course of an hour it became broad at the point, and 
a new branch broke out. From these changes 
Herschel concluded that the shallows are occasion- 
ed by something issuing from the openings, which 
drives away the luminous clouds from the parts 
where it finds the least resistance, or which dis- 
solves these clouds as soon as it reaches them. 
The new branch afterwards began to increase, and 
another branch, marked H, fig. 9, began to break 
out from the shallow around E. These changes 
Dr. Herschel attributed to the gas or substance 
which at first forced open the passages and was 



12. 



11. 



^ 



13. 






c-4 




then widening them. Three small branches, a, b, c, 
were seen to project from the shadow of the large 



opening in fig. 12. The vacancies between these 
branches were afterwards filled up by the same 
cause that occasioned them, so as to increase the 
breadth of the shallow on that side of the opening. 
The shallows have no corrugations, but are tufted, 
like masses of dense clouds. The decay of the 
shallows is supposed to arise from the encroach- 
ment of the luminous clouds, in consequence of the 
enfeebled energy of the gas or substance that pro- 
duced them. 

Ridges are elevations of the luminous clouds 
above their general level, or above the general sur- 
face of the sun. These elevations generally sur- 
round openings, though they have sometimes been 
perceived where openings do not exist. Ridges 
soon disperse. One of them occupied a space 
which subtended an angle of 2' 46", corresponding 
to 75,000 English miles. Herschel ascribed the 
formation of the ridges to the disturbance of the 
luminous clouds, by the elastic gas which issues 
from the openings ; or he conceived that this gas 
may act below the luminous clouds, so as to elevate 
them above their ordinary level. 

Nodules, formerly called faculae or luculi, are 
small, but brilliant and highly elevated parts of the 
luminous clouds. Dr. Herschel imagined that they 
may be ridges, seen obliquely or foreshortened. 

Corrugations are elevations and depressions of 
the luminous matter, having a mottled appearance, 
and consisting of light and dark places. The dark 
places appear to be lower than the bright places ; 
and, in a favorable atmosphere, the corrugations 
may be as distinctly perceived as the rough surface 
of the moon. They extend over every part of the 
sun's surface. Their shape and position is per- 
petually changing, and they increase, diminish, 
divide and vanish quickly. 

Indentations are the dark parts of corrugations ; 
and, from the circumstance of their being visible 
very near the limb of the sun, it would appear that 
they are not much depressed below the level of the 
luminous clouds. The sides of the indentation are 
like circular arches, (fig. 13,) with their bottoms 
occasionally flat. Indentations are of the same 
nature with shallows, varying in size, and some- 



112 



WONDERS OF THE HEAVENS 



times containing small openings, and at other times 
changing into openings. They extend over the 
whole surface of the sun, and with small magnify- 
ing powers they have the appearance of points. 

Pores are small holes or openings in the low 
places of indentations. Sometimes they increase 
and become openings, and frequently vanish in a 
short time. 



We give below a telescopic view of the sun, 
exhibiting the daily appearance of several remarka- 
ble spots, that have appeared at various times on 
his surface, the appearance for a day being contain- 
ed by two lines drawn at right angles, or nearly so, 
to the direction of the spots' motion, which is from 
right to left in the plate, or on the sun's disc from 
the eastern to the western edge. 




From the interesting facts above given, Herschel 
deduced a theory of the solar phenomena, which, 
however ingenious it may be, is founded on assump- 
tions too arbitrary and gratuitous to be recognised in 
a science which admits of no evidence but demonstra- 
tion. To suppose that the numerous irregularities 
on the surface of the sun are occasioned by an elas- 
tic empyreal gas, which rises through the openings 
and disturbs the equilibrium of the luminous mass, 
is to show how these irregularities may be produced 
by the action of a hypothetical agent ; but it never 
can be considered as an explanation of the process 



which nature is carrying on in that immense deposi- 
tory of fire. But though we cannot admit the hypo- 
thesis proposed by this learned and ingenious astro- 
nomer, we are disposed to acquiesce in some of 
the important conclusions which he drew from his 
observations. From the numerous elevations and 
depressions of the luminous matter, and from the 
length of time during which they are visible, Her- 
schel justly inferred that the shining matter of the 
sun is not a fluid, but a mass of luminous or phospho- 
ric clouds. He conceived, from the uniformity of 
color in the shallows, that below these self-luminous 



WONDERS OF THE HEAVENS. 



113 



clouds there is another stratum of clouds of inferior 
brightness, which is intended as a curtain to protect 
the solid and opaque body of the sun from the 
intense brilliancy and heat of the luminous clouds. 
By means of his photometer, Dr. Herschel found 
that the light reflected by the inferior clouds is 
four hundred and sixty-nine out of one thousand ; 
and that the light reflected by the opaque body of 
the sun is only seven. Hence it appears that the 
sun consists of a dark solid nucleus, surrounded by 
two strata of clouds. The outermost of these is the 
region of that light and heat which is diff"used from 
the centre to the remotest parts of the system, 
while the interior stratum is supposed to protect 
the inhabitants of the sun from the fiery blaze of 
the stupendous furnace by which they are inclosed.* 
That the sun may at the same time be the source 
of light and heat, and yet capable of supporting 
animal life, is one of those conclusions which we 
are apt to admit without hesitation, and to cherish 
with peculiar complacency. The mind is filled 
with admiration of the wisdom of God, and swells 
with the most sublime emotions, when it conceives 
that apparently the most inaccessible regions of 
creation are peopled with animated beings, and that 
while the sun is the fountain of the most destructive 
of the elements, it is at the same time the abode of 
life and felicity. In impressions of this kind, how- 

* The opinions of Dr. Herschel respecting the nature of the sun 
were maintained some 5'ears earlier in England by Dr. Elliot, who 
was tried at the Old Bailey for the murder of Miss Boydell. The 
friends of the doctor maintained that he was insane, and called seve- 
ral witnesses to establish this point. Among them was Dr. Simmons,' 
who declared that Dr. Elliot had for some months before shown a 
fondness for the most extravagant opinions ; and that in particular 
he had sent to him a letter on the light of the celestial bodies, to 
be communicated to the Royal Society. This letter confirmed Dr. 
Simmons in the belief that this unhappy man was under the influ- 
ence of mental derangement ; a\id as a proof of the correctness of this 
opinion he directed the attention of the court to a passage of the letter 
in which Dr. Elliot states " that the light of the sun proceeds from a 
dense and universal aurora, which may afford ample light to the in- 
habitants of the surface (of the sun) beneath, and yet be at such a dis- 
tance aloft as not to annoy them. No objection," says he, " ariseth to 
that great luminary being inhabited : vegetation may obtain there as 
well as with us. There may be water and dry land, hills and dales, 
rain and fair weather ; and as the light, so the season must be eter- 
nal ; consequently, it may easily be conceived to be by far the most 
blissful habitation of the whole system." 
15 



ever, delightful though they be, we must not rashly 
indulge, lest we should afterwards find that we 
have been admiring an orcjer of things which does 
not exist in nature, and have thus been indirectly 
reflecting on the infinite wisdom that sanctioned an 
opposite arrangement. Whenever we allow our 
feelings to interfere with our reasonings, we are 
apt to yield ourselves to the guidance of loose ana- 
logies and imperfect views, and become the defend- 
ers of opinions which every subsequent observation 
and discovery will only tend to overthrow. We 
conceive that the opinion of the sun's being a habit- 
able globe rests on reasonings of this nature ; and 
as the subject is curious and worth examination, we 
shall endeavor to place it in its proper light. 

When the invention of the telescope enabled 
astronomers to detect the striking resemblances 
between the different planets of the system, it was 
natural to conclude that, as they were composed of 
similar materials, as they revolved around the same 
centre, and were enlightened by similar moons, 
they were all intended by their wise Creator to 
be the region in which he chose to dispense the 
blessings of existence and intelligence to various 
orders of animated beings. The human mind cheer- 
fully embraced this sublime view of creation ; and, 
guided by the principle that nothing was made in 
vain, man extended his views to the remotest 
corners of space, and perceived in every star that 
sparkles in the sky the centre of a new system of 
bodies, teeming with life and happiness, and dis- 
playing fresh instances of the power and beneficence 
of their Maker, Having thus traversed the illimi- 
table regions of space, and considering every world 
which rolls in the immense void as the scene on 
which the Almighty has exhibited his perfections, 
the mind, unable to command a wider range, rests 
in satisfaction on the faithful analogies that it has 
pursued. While the planets were thus regarded 
as habitable worlds, astronomers considered the 
sun and the stars as the reservoirs from which light 
and heat were dispensed to man, and as the great 
central magnets that bound together, and guided 
in their course, the various planets which surround 
them. These offices were reckoned sufficient for 



114 



WONDERS OF THE HEAVENS 



the great luminary ; and astronomers were led, by- 
no analogy and by no consideration of final causes, 
to view it as the seat of animal existence ; they left 
it to the poets to people with a colony of salaman- 
ders these regions of eternal fire. 

The solar observations of Dr. Wilson first sug- 
gested the opinion that the sun was an opaque and 
solid body, surrounded with a luminous atmosphere, 
and the telescopes of Dr. Herschel have tended 
still farther to establish this opinion. The latter 
of these astronomers, therefore, imagined that the 
functions of the sun, as the source of light and heat, 
might be performed by the agency of its external 
atmosphere; while the solid nucleus was reserved 
and fitted for the reception of inhabitants. This 
conjecture, however, is consonant with nothing 
which we find in nature. It is inconceivable, in- 
deed, that luminous clouds, yielding to every im- 
pulse, and in a state of perpetual change, could be 
the depository of that devouring flame, and that 
insupportable blaze of light, which are emitted by 
the sun ; and it is still more inconceivable that the 
feeble barrier of planetary clouds could shield the 
subjacent mass from the destructive elements that 
raged above. 

If we inquire (says Dr. Young) into the intensity 
of the heat that must necessarily exist wherever 
this combustion is performed, we shall soon be con- 
vinced that no clouds, however dense, could impede 
its rapid transmission to the parts below. Besides, 
the diameter of the sun is one hundred and eleven 
times as great as that of the earth ; and at its sur- 
face a heavy body would fall through no less than 
four hundred and fifty feet in a single second ; so 
that, if every other circumstance permitted human 
beings to reside in it, their own weight would pre- 
sent an insuperable difficulty, since it would become 
thirty times as great as upon the surface of the 
earth, and a man of moderate size would weigh 
above two tons. Again, the quantity of heat that is 
transmitted to the habitable regions of the sun, for 
the purposes of vegetation, must necessarily accu- 
mulate, till it becomes insupportable, as there is 
no possibility of its escaping back to the luminous 
atmosphere. 



The opacity of the interior globe of the sun is no 
reason why it may not act a part in the production 
or preservation of the solar heat. On the contrary, 
it appears highly probable and consistent with 
other discoveries, that the dark solid nucleus of the 
sun is the magazine from which its heat is discharg- 
ed, while the luminous or phosphorescent mantle, 
which the heat freely pervades, is the region where 
its light is generated. Herschel's own experiments 
assure us, that invisible rays, which have the power 
of heating, and which are totally distinct from those 
that produce light, are actually emitted from the 
sun ; and that luminous rays incapable of producing 
heat are discharged from the same source. These 
facts, therefore, not only confirm the theory which 
we have stated, but receive in return from that 
theory the most satisfactory explanation. The in- 
visible rays which pervade every part of the solar 
spectrum formed by a prism, and which extend be- 
yond its red extremity, are emitted from the opaque 
nucleus, and therefore excite no sensation of light 
on the human retina ; while the colored rays, which 
form the spectrum itself, are discharged from the 
luminous matter that encircles the solid nucleus, 
and are therefore endowed with the property of 
illumination. Hence it is easy to assign the reason 
why the light and heat of the sun are apparently 
always in a state of combination, and why the one 
emanation cannot be obtained without the other. 
The heat projected from the dark body, and the 
light emitted from the luminous atmosphere, are 
thrown off in lines diverging in every possible 
direction ; so that the two radiations must be uni- 
formly intermingled, and, as in a stream flowing 
from two contiguous sources, the heat must always 
accompany its kindred element. That light and 
heat are two different substances, distinguished by 
different properties, is a proposition which seems 
to flow from the most recent experiments. We 
find the invisible heat of the sun existing separately 
from its light, and possessing a degree of refrangi- 
bility less than the least refrangible rays of the 
prismatic spectrum. Light has likewise been found 
separate from heat, and though it may be imagined 
that this arises from the extreme attenuation of the 



a CMB.'.IMl^'gW 



WONDERS OF THE HEAVENS 



115 



light, yet, when the light of the moon is concen- 
trated by powerful burning mirrors, we ought cer- 
tainly to have expected that the heat, if any did 
exist, would be appreciable by delicate thermome- 
ters. Every attempt, however, to detect heat in 
the rays of the moon has completely failed, and we 
are therefore entitled to presume that a greater 
proportion of heat than of light has been absorbed 
by that luminary. If light and heat, then, be two 
different substances, endowed with different chemi- 
cal and physical properties, is it not unphilosophical 
to suppose that they are emitted from the same 
source, when we have actually two different regions 
in the sun, to which we can with more propriety 
refer their origin 1 

This opinion, which is proposed only as a con- 
jecture, founded on the most probable analogies, 
will receive considerable confirmation if we can 
adduce any strong analogical arguments against the 
supposition that the sun is a habitable world; for 
if the nucleus is not fitted for the reception of 
living beings, it is the more probable that it acts a 
capital part in the production or preservation of the 
solar heat. Some arguments have already been 
suggested relative to this point. We shall endeavor 
to illustrate two other considerations, which, we 
trust, will have some weight in favor of this opinion. 
Since those w^ho consider the sun as a habitable 
world found this opinion upon analogical argu- 
ments, we are entitled to avail ourselves of all the 
assistance which can be drawn from the same 
source. If the sun, then, be a great habitable 
planet, we may expect to find in it those points of 
resemblance to the other planets which are re- 
garded as distinctive marks of a habitable world; 
and if we shall find that any analogy, which subsists 
with respect to all the other planets, fails when 
applied to the sun, we are entitled to consider this 
difference as a proof that the sun is not inhabited. 

In proceeding from the remotest of the planets 
to the centre of the system, we find that a general 
law prevails respecting the densities of the planets. 
These densities appear to increase as the planet is 
nearer the sun. With the single exception in the 
case of the planet Herschel, whose density is not 



yet accurately ascertained, the densities uniformly 
increase according as the habitable world ap- 
proaches to the centre of light and heat. We 
should therefore have expected, from analogy, that 
the habitable part of the sun would have exceeded 
Mercury in density, because it is nearer than that 
planet to the source of light and heat. This, how- 
ever, is far from being the case ; the density of the 
sun is only a little greater than the density of 
water. Here then we have a complete breach in 
the analogy which we anticipated; and it is no 
objection to this argument to say, that the situation 
of the sun, in the centre of the system, may exempt 
it from the general law of density ; because this is 
a virtual admission that analogical reasoning, on 
which Herschel's opinion is founded, cannot be 
fairly applied in such a case. 

If the sun is a habitable globe, we can scarcely 
avoid drawing the conclusion, with Dr. Elliot, that 
"it must be by far the most blissful habitation in 
the whole system." We should expect, at least, 
that the solar inhabitants would be rational beings, 
endowed with intelligence equal to that of man, 
and availing themselves of their central position to 
study the interesting phenomena of the various 
planets which revolve around them, and of the 
numerous suns which their own globe would seem 
to resemble. If there is one place in the system 
more than another where astronomy could be 
studied with the greatest facility and carried to 
the highest perfection, that place would be in the 
sun, where, excepting the phenomena arising from 
its monthly rotation, the real and apparent motions 
of the heavenly bodies must be exactly the same. 
But these results of analogy are mere illusions of 
the mind. Nature has drawn an impenetrable 
curtain between the inhabitants of the sun and the 
worlds which circulate around them: she has 
doomed them to the most solitary dwelling in the 
whole circle of creation, and has marked them as 
either unfit or unworthy to enjoy the noblest 
privileges of intelligent beings. The planets and 
the stars are equally invisible from the surface of 
this luminary, unless when a transient glimpse of 
the . heavens is obtained through an accidental 






l£^ 



116 



WONDERS OF THE HEAVENS. 



opening in the solar atmosphere. From the year 
1676 to the year 1684 there was not a single spot 
in the sun's atmosphere ; so that during eight suc- 
cessive years the inhabitants of that globe, if they 
do exist, never once obtained a glimpse of that 
starry firmament, from the contemplation of which 
a Supreme Being could scarcely have excluded any 
of his rational creatures. 

To maintain, therefore, that the sun is peopled 
by intelligent beings, is to reason in defiance of the 
strongest analogies, and support opinions which 
posterity will rank among the aberrations of the 
human mind. Might we not as well suppose that 
the central caverns of our own planet, which cos- 
mogonists have filled with fire or with water, are 
the abode of a rational population, who, like the 
inhabitants of the sun, are occasionally permitted 
to obtain a transient view of the heavens through 
the craters of volcanoes, or the chinks and fissures 
which may accompany the convulsions of the globe ? 

Before concluding our remarks on the construc- 
tion of the sun, we must take notice of another 
opinion of Herschel's respecting the solar spots, 
which has been less generally received than that 
which we have been combating. Imagining that 
the luminous atmosphere of the sun is the region of 
light and heat, he concluded that when the ridges, 
corrugations and openings in this atmosphere are 
numerous, the heat emitted by the sun must be 
proportionally increased, and that this augmenta- 
tion must be perceptible by its effects upon vegeta- 
tion. He expected, therefore, that in those years 
when the solar spots were most numerous vegeta- 
tion would be most luxuriant, and that this effect 
might be ascertained from the price of wheat, as 
marking the productiveness of the season. By 
comparing the solar appearances as given by La 
Lande with the table of the price of wheat in 
Smith's Wealth of Nations, he obtained results 
which, on the whole, appear favorable to his hypo- 
thesis. We do not readily see upon what principle 
Herschel concluded that the existence of spots in- 
dicates an abundance of luminous matter. We 
should rather have been disposed to think that, in 
proportion to the number and magnitude of the 



openings, the light and heat of the sun would have 
been diminished, as so much of the sun's surface is 
then disqualified for the discharge of its usual func- 
tions. If there is really an increased luxuriance of 
vegetation in those years when the solar openings, 
&c. are most numerous, (an opinion which we are 
much disposed to call in question,) we conceive that 
the theory which we have already explained affords 
a very satisfactory explanation of the fact. The 
heat being supposed to be emitted from the dark 
body of the sun, it is obvious that when there is any 
opening in his luminous atmosphere, the heat 
emanating from the internal nucleus must be more 
copiously discharged, in consequence of receiving no 
obstruction from the luminous clouds ; or if we re- 
gard the variations in the sun's surface as produced 
by variations in the heat which rises from the 
nucleus, we may naturally suppose that, when the 
heat of the sun is most intense, it will produce the 
greatest changes in the luminous atmosphere. 

Herschel invented a very ingenious contrivance 
for moderating the heat and light of the sun, when 
it is examined by means of powerful telescopes. 
He abandoned the common method of using dark 
colored glasses, and had recourse to fluids. For 
this purpose, he employed a small square trough, 
having in two of its opposite sides well polished 
plates of glass. A small handle on one side of the 
trough, and a spout on the other, were made for 
the purpose of pouring out any portion of the liquid, 
when the rest was to be diluted. The trough was 
then placed in an excavation in the eye-piece of the 
telescope, so that the rays of the sun might pass 
through the fluid before they reached the eye of the 
observer. By coloring the fluid, the light may be 
softened at pleasure, and the heat is completely 
removed by the water. Herschel found that ink, 
diluted with water and filtered through paper, gave 
a distinct image of the sun, as white as snow. By 
this mixture he could observe the sun in the meri- 
dian without the smallest injury to his eye or to 
the glasses, even when he used a mirror nine 
inches in diameter, and when the eye-pieces were 
open, as in night observations. 

As the phenomenon called the zodiacal light has 



WONDERS OF THE HEAVENS 



n? 



been generally supposed to arise from the sun's 
atmosphere, we consider this as the proper place 
for giving an account of the appearance. Though 
this light seems to have been observed by Descartes 
and by Childrey about 1659, yet it did not attract 
general notice till the year 1693, vv^hen it was ob- 
served by Cassini, and received its present name. 
The zodiacal light, which is less bright than the 
milky-way, is seen at certain seasons of the year 
before the rising and after the setting of the sun. 
It resembles a triangular beam of light, rounded a 
little at the vertex. Its base is turned towards the 
sun, and its axis is inclined to the horizon, and lies 
in the direction of the zodiac. The vertical angle 
of this luminous cone is sometimes twenty-six de- 
grees and sometimes ten degrees ; its length, reckon- 
ing from the sun, which is its base, is sometimes 
forty-five degrees, and at other times one hundred 
and fifty degrees. Pingre saw one, in the torrid 
zone, which was one hundred and twenty degrees 










long, and whose horizontal breadth was from eight 
degrees to thirty degrees. The best time for see- 
ing the zodiacal light is about the first of March, at 



seven o'clock in the evening, when the twilight is 
ending, and the equinoctial point in the horizon. 
The luminous triangle will then appear to be 
directed towards Aldebaran, as in the plate, its axis 
forming an angle of sixty-four degrees with the 
horizon : but if it is viewed in the morning, before 
sunrise, the angle which it makes with the horizon 
will be only twenty-six degrees. In the year 1781, 
Flauzeres observed it in the month of January. 
On the 21st of March, at half past seven o'clock, it 
ended beyond the Pleiades, and was sixty-one de- 
grees long, ten and a half broad, and eight high. 
According to Foulquier, the zodiacal light is always 
seen at Guadaloupe, unless when the weather is 
bad. Humboldt observed the zodiacal light at 
Caraccas on the 18th of January, after seven P. M. 
The point of the pyramid was at the height of fifty- 
three degrees. The light totally disappeared at 
9h. 35' apparent time, about 3h. 50' after sunset, 
without any diminution in the serenity of the sky. 
On the 15th of February it disappeared 2h. 50' after 
sunset; and the altitude of the pyramid was fifty 
degrees on both those occasions; the intensity of 
the zodiacal light varied in a very sensible manner, 
at intervals of two or three minutes. These 
changes took place in the whole pyramid, espe- 
cially towards the interior, far from the edges ; 
sometimes the light was very faint, and some- 
times it exceeded that of the milky-way in Sagit- 
tarius. 

As this phenomenon uniformly accompanies the 
sun, it has been naturally ascribed to an atmo- 
sphere round this luminary, extending beyond the 
orbit of Mercury, and sometimes even beyond that 
of Venus. The zodiacal light is supposed to be a 
section of this atmosphere, which, being extremely 
flat at its poles, cannot be supposed to partake of 
the sun's monthly motion. La Place has shown that 
the sun's atmosphere cannot reach even the orbit 
of Mercury, and that it could not in any case dis- 
play this particular form. Dr. Young remarks, 
that the only probable manner in which it can be 
supposed to retain its figure, is by means of a 
revolution much more rapid than the sun's rotation. 
Some philosophers have ascribed the phenomenon, 



118 



WONDERS OF THE HEAVENS 



without any reason, to the refraction of the earth's 
atmosphere.* 

Besides the revolution of the sun round his axis 
in twenty-five days, and his irregular motion about 
the centre of gravity of the solar system, he ap- 
pears to have a progressive motion in absolute 
space. As all the bodies of the system necessarily 
partake of this motion, it can only be perceptible 
from a change in the position of the fixed stars, to 
which the system is advancing or from which it 
recedes. This change of place, or proper motion in 
the fixed stars, as it has been called, was first ob- 
served by Halley, and afterwards by Le Monnier. 
Mager, however, advanced a step farther than 
these astronomers. He compared the places of 
about eighty stars, as determined by Roemer, with 
his own observations, and he found that the greater 
number of them had a proper motion. He was 
aware that this change of place might be explained 
by a progressive motion of the sun towards one 
quarter of the heavens: but as the result of his 
observations does not accord with this hypothesis, 
he remarks that many centuries must elapse before 
the true cause of this motion is explained. Dr. 
Wilson suggested, upon theoretical principles, the 
possibility of a solar motion, and La Lande deduced 
the same opinion from the rotary motion of the sun. 
But these conjectures have been almost completely 
confirmed by another species of argument. 

If the sun has a motion in absolute space direct- 
ed towards any quarter of the heavens, it is obvious 
that the stars in that quarter must appear to re- 
cede from each other, while those in the opposite 
region seem gradually approaching. The proper 
motion of the stars, therefore, in those opposite re- 
gions, as ascertained by a comparison of ancient 
with modern observations, ought to correspond 
with this hypothesis. 

* For a farther account of the zodiacal light, see chapter X. 



Herschel examined this subject, with his usual 
success, and he certainly discovered the direction 
in which our system is gradually advancing. He 
found that the apparent proper motion of about 
forty-four stars, out of fifty-six, are very nearly 
in the direction which should result from a motion 
of the sun towards the constellation Hercules. 

By considering the motion of the satellites around 
their primary planets, and of the primary planets 
around the sun. Dr. Herschel supposed that the 
proper motion of the sun is not rectilineal, but 
that it is performed around some distant and un- 
known centre. Just, however, as the conception 
appears to be, we can scarely allow ourselves to 
think that there is an immense central body, of 
sufficient magnitude to carry around it all the sys- 
tems with which astronomers have filled the regions 
of space : but we may suppose, with La Lande, that 
there is a kind of equilibrium among all the sys- 
tems of the world, and that they all have a peri- 
odical circulation around their common centre of 
gravity. 

We ought to add, that Herschel's theory, as far 
as regards the existence of a luminous atmosphere 
round the sun, appears to be confirmed by an ex- 
periment reported to the French Academy in 1824. 
Fourrier had proved, by certain experiments upon 
the polarization of luminous rays, that those which 
escaped from a metallic sphere heated to a red 
heat possessed this property ; but those which 
proceeded from a gaseous sphere heated to a white 
heat were destitute of it. Arago tried the experi- 
ment with the solar light, and, finding that it did not 
possess the property of polarization, admitted, as a 
consequence of this result, that the medium, whence 
the solar ray proceeded, did not essentially differ 
from an elastic fluid, and that, consequently, there 
existed around the sun an incandescent atmo- 
sphere. 



CHAPTER IV. 



SECTION I, 



Horizontal moon — An illusion — Mode of estimating distances — Varia- 
tion of the moon's distance from the earth — Motion from west 
to east — Amount of motion per day — Per minute — Moon's nodes 
— Syzygies — Lunar cycle — Golden number — The moon's periodic, 
synodic and sidereal revolution — Disturbance of the moon's orbit. 

We may observe that in proportion as the moon 
rises above the horizon its apparent diameter 
changes. To our eyes it appears to be largest at 
the horizon, when, in fact, from its being more 
distant by the semidiameter of the earth, it ought 
on this account to appear actually smaller. This 
difference of distance in regard to the sun and stars 
is so small in comparison with their whole distance, 
that it may be left out in considering their diame- 
ters. But with the moon it is not so ; and the 
apparent diameter at the zenith must be about 
sixteen seconds greater than at the horizon. 

Yet, if we observe the moon with the naked eye, 
our observation would reverse this fact. Our sight 
contradicting the results of the micrometer, we 
judge the moon and sun larger at their rising. 
This is an illusion to be removed. The constella- 
tions, also, when near the horizon seem to occupy a 
greater extent in the heavens. We shall explain 
this singular error of our senses. 

At the same time that experience teaches us 
how to use the image of an object on the retina of 
the eye in estimating the form of that object, it 
teaches us to form an estimate of its position in 
space, its size and distance; and if the distance is 
so great that the hand cannot reach, we approach 
the object until we can touch it, and then, removing 
from it, we judge of its distance by the extent of 
motion required in us to approach or recede from 
it. When, afterward, we wish to estimate the dis- 
tance of any body situated so that we cannot ap- 
proach to its touch, the distance of some object 
previously determined is taken as a scale of mea- 
surement. But in proportion as the distance in- 
creases, the circumstances under which we judge 



become less favorable, and beyond a certain limit 
objects are presented to us under appearances more 
or less deceitful, and we are led into optical errors. 

In estimating the distance, then, of an object, we 
must take into consideration the angle under which 
we see it, the diminution of the tints caused by 
its distance, its real magnitude, the intermediate 
bodies, which serve as points of comparison, — cir- 
cumstances that we may be skilled in estimating 
within certain limits, but which beyond those limits 
are constant causes of deception. 

We cannot judge of the distance of a mountain 
or a ship, unless we have often passed over similar 
intervals ; the want of intermediate objects deprives 
us of the means of comparison. 

At the rising of the moon, terrestrial objects are 
the points of comparison, which fail us when she is 
in the zenith. The heavens seem to us more dis- 
tant at the horizon than at the zenith, and thus 
present in appearance an elliptical arch. This is 
an involuntary effect of habit ; we cannot resist it, 
any more than the broken appearance of a staff, 
plunged obliquely into water. We are carried 
aAvay by the invincible power of our senses. 

Now the optical angle remaining the same, if we 
judge the moon much more remote, it ought in the 
same proportion to appear larger to us. This de- 
ception is confirmed also by its diminution of light 
at the horizon. Its rays, traversing an extensive 
and misty portion of the atmosphere, present to us 
the appearance of light enfeebled by greater dis- 
tance from us. 

The moon is in reality a little more distant Avhen 
in the horizon, and consequently its diameter is a 
little less. If our senses tell us otherwise, the 
error may be corrected by looking at that body 
through a tube or a smoked glass, so fixed as to 
conceal all other objects which might serve as 
terms of comparison. 

From the apparent diameters of the moon we 
may deduce the variations of its radius vector, or of 



120 



WONDERS OF THE HEAVENS. 



its distance from the earth, around which it revolves 
in an elliptical orbit from west to east. While the 
earth describes the ecliptic in a year in the direc- 
tion PEA, around the sun S, the moon M describes 




an ellipse MO about the earth E, situated in one 
of its foci. This ellipse is movable, being carried 
with the earth around the sun every year; the 
moon in the mean time going through its ellipse 
thirteen and a half times. By measuring the 
greatest latitude of the moon, it has been found 
that its orbit is inclined 5° 9' to the plane of the 
earth's orbit. 

The appearances are to us the same as if, our 
globe being stationary, the moon described its orbit 
around us in about twenty-seven days, while the 
sun travels in an orbit four hundred times more re- 
mote, in about three hundred and sixty-five days, 
the earth seeming to be fixed in a focus common to 
the two ellipses, and turning on its axis in twenty- 
four hours. This rotation of the earth makes us 
attribute to the heavenly bodies a daily revolution 
from east to west. During this time, the moon 
moves on in its orbit, in reality from west to east, 
describing arcs of variable lengths, which, as seen 
from the earth and measured in the heavens, have 
a mean value of 13° IV. The sun's apparent daily 
motion in the ecliptic is but one degree, or ^V of the 
moon's mean daily motion in her ellipse. The 
variation of declination of these bodies is the cause 
of the changes in their rising, setting and meridian 
altitudes. The motion in their orbits toward the 
east is the cause of the daily retardation in the 
time of their transit over the meridian. 

The velocity of the moon's motion is thirty-nine 
miles a minute, or sV of that of the earth in its 
orbit, that being 1133^ miles a minute. But in 



estimating the rapidity of the moon, we ought to 
unite these two motions, since, as we have said be- 
fore, the moon accompanies the earth around the 
sun. Thus the absolute rapidity of the moon's 
motion is from 1094 miles to 1172 miles a minute, 
according to its position. 

The planes of the lunar and terrestrial ellipses 
cut each other in two points, called the nodes 
(crossings) of the moon's orbit. 

The moon is sometimes on one side and some- 
times the other side of the plane of the ecliptic. 
The point where the moon crosses this plane when 
approaching the north pole is called the ascending 
node. The point where it crosses the same plane 
when going south is called the descending node. 
The line joining these points is named the line of 
the nodes. These points vary their position at each 
revolution of the moon, the line of the nodes being sub- 
ject to a slow motion of revolution from east to west, or 
in a direction contrary to the order of the signs of the 
zodiac. Every year the nodes describe about 
19F, which gives one degree for every nineteen 
days, or 1° 28' for a lunar month, or, finally, an 
entire revolution in eighteen and a half years. 

Not only does the line of the nodes revolve in 
the plane of the ecliptic, but the lunar ellipse 
changes a little its inclination to this plane, 
librating slowly above and below a mean position. 
In the plane of this movable orbit, the line of the 
syzygies (i. e. the line joining the points nearest and 
farthest from the earth) revolves around our globe. 

During nineteen years, there occur two hundred 
and thirty-five lunations; and after this space of 
time, new and full moons recur at the same date 
as before. The solar year is eight days more than 
twelve lunations, which form the lunar year. These 
eight days accumulating, there result, after nineteen 
years, seven lunations to be added to the two hun- 
dred and twenty-eight, which allow but twelve for a 
year. Out of these nineteen years, then, seven, 
which are called embolismic, (intercalary,) must 
have thirteen new moons, instead of twelve, and 
one of the months must have two new moons. 

It follows, that if we have a series of lunar ob- 
servations during nineteen years, the phases would 



WONDERS OF THE HEAVENS. 



121 



return periodically at the same dates. Of this 
number (nineteen) consists the cycle of Meton, also 
called the golden number, because the Athenians, 
in their admiration of the properties of the lunar 
cycle, engraved the discovery of it in letters of 
gold. One year of this cycle w^ill have a new moon 
on the first of January. 

There may be constructed, then, by aid of atten- 
tive observations for nineteen years, tables of the 
lunar phases and motions, which will return peri- 
odically in the same order, and may be predicted 
by the use of these tables. 

We have stated, that the moon moves round the 
earth from west to east. The sun apparently moves 
in the same direction, but is much longer in com- 
pleting an entire revolution than the moon. It is 
evident, therefore, that if the sun and moon are at 
some one instant in the same direction with respect 
to the earth, the moon will continually outstrip 
him, until she returns to the same place at which 
we suppose her to have been when they were ob- 
served together. When she arrives there, the sun 
will be there no longer, but at some distance to the 
eastward of that position, and the moon will have to 
go on for some time longer before she overtakes 
him, and is again seen in the same direction with 
him. Her time of returning to this point in her 
orbit, from which we have supposed her to set out, 
or of making a complete revolution round the earth, 
is called her j9enoc?fc time; her time of being again 
in the same direction with the sun is called her 
synodic revolution, or period, from a Greek word, 
meaning a coming together. The synodic period may 
be determined by observation ; and the best mode 
of doing so is by the observation of eclipses of the 
moon. The nature of these phenomena will be 
explained hereafter ; they are easily observed, and 
the middle of the eclipse is very near the time at 
which the earth is directly between the sun and 
moon, and that exact time may be easily computed 
from the observations made of the eclipse. From 
one of these times, therefore, to another, or from the 
commencement or close of one eclipse to those of 
another happening under similar circumstances, (for 

then, in each case, the moon will be in the same 
16 



position with respect to the earth,) is necessarily 
either one synodic period of the moon, or some 
exact number of synodic periods : and if the time 
at which each takes place be observed, the interval 
between them, divided by the number of synodic 
revolutions, will give the length of the synodic 
period. If the eclipses are taken at the same, or 
very nearly the same period of the year, the moon 
and sun will each of them be nearly in the same 
position with respect to the earth at each observa- 
tion, or each will have revolved a certain number 
of times round the earth ; and, consequently, as the 
principal inequalities of the motion of each are gone 
through in the space of one revolution, each will 
have gone through all the varieties of its motion a 
certain number of times, and may therefore be con- 
sidered as having passed through the same space as 
if it had always moved with its mean motion. The 
synodic period therefore, thus deduced, will be the 
mean synodic period ; except indeed that the motion 
of the moon's apogee, being considerable, must not 
be entirely left out of the account, as the rate of 
her motion in her orbit depends on her situation 
with relation to that point. To make the correct- 
ness of the result deduced complete, therefore, we 
should add the further condition that the apogee of 
the moon should be about the same place at each 
observation. It would not, however, be easy to 
find observations so fully corresponding to each 
other. If, however, we take observations very dis- 
tant from each other in time, the apogee will have 
revolved a certain number of times, and in each of 
these revolutions the moon will have had all her 
varieties of motion ; there will besides be one in- 
complete revolution of the apogee, and one only, 
occasioning some deviation from the mean value. 
Still the error thus produced will be divided among 
all the synodic periods included between the two 
observations, and will therefore produce very little 
effect on each ; and on the same principle, if the 
time intervening be great enough, even the ine- 
qualities produced by observing at different seasons 
of the year may be neglected. 

Nov*^ eclipses are phenomena so remarkable, that 
they have been very long observed ; and the time 



122 



WONDERS OF THE HEAVENS. 



of the occurrence of some has been recorded with 
sufficient accuracy even before the Christian era. 
By comparing these with recent observations, made 
at the same season of the year, the duration of the 
mean synodic period may be ascertained with very 
great accuracy; and it is thus found to be 29d. 12h. 
44m. 2s. 8. 

But 27d. 7h. 43 m. lis. 51 is the sidereal revolution 
of the moon, — her time of describing three hundred 
and sixty degrees, or of returning to the same posi- 
tion with respect to the stars. But while she per- 
forms her revolution, the equinox will have retro- 
graded, and her return to the same position with 
respect to the equinox, or her tropical period, will 
be shorter. It is in fact but 27 d. 7h. 43 m. 2s. 
and -- 



TS. 



These results do not help to explain the most 
remarkable appearances of the moon, or those to 
which the attention of a common observer is first 
directed ; and we therefore shall proceed in the 
next section to state the nature of those appear- 
ances, and to explain the cause from which they 
proceed. But we shall stop here to make a few 
general remarks, which, we hope, may not be un- 
interesting or out of place. 

The best way to form a distinct conception of the 
moon's motion is to regard it as describing an 
ellipse about the earth in the focus, and, at the 
same time, to regard this ellipse itself to be in a 
twofold state of revolution: 1st, in its own plane, 
by a continual advance of its axis in that plane ; and 
2dly, by a continually tilting motion of the plane 
itself, exactly similar to, but much more rapid than, 
that of the earth's equator, produced by the conical 
motion of its axis. 

The physical constitution of the moon is better 
known to us than that of any other heavenly body. 
By the aid of telescopes, we discern inequalities in 
its surface which can be no other than mountains 
and valleys — for this plain reason, that we see the 
shadows cast by the former in the exact proportion, 
as to length, which they ought to have, when we 
take into account the inclination of the sun's rays 
to that part of the moon's surface on which they 
stand. The convex outline of the limb turned 



towards the sun is always circular, and very nearly 
smooth ; but the opposite border of the enlightened 
part, which (were the moon a perfect sphere) ought 
to be an exact and sharply defined ellipse, is always 
observed to be extremely ragged, and indented 
with deep recesses and prominent points. The 
mountains near this edge cast long black shadows, 
as they should evidently do, when we consider that 
the sun is in the act of rising or setting to the parts 
of the moon so circumstanced. But as the enlight- 
ened edge advances beyond them', i. e. as the sun to 
them gains altitude, their shadows shorten ; and at 
the full moon, when all the light falls in our line of 
sight, no shadows are seen on any part of her sur- 
face. From micrometrical measures of the lengths 
of the shadows of many of the more conspicuous 
mountains, taken under the most favorable circum- 
stances, the heights of many of them have been calcu- 
lated. The existence of such mountains is corrobo- 
rated by their appearance as small points or islands 
beyond the extreme edge of the enlightened part, 
which are their tops, catching the sunbeams of light 
before the intermediate plain, and which, as the 
light advances, at length connect themselves with it, 
and appear as prominences from the general edge. 
The generality of the lunar mountains present a 
striking uniformity and singularity of aspect. They 
are wonderfully numerous, occupying by far the 
larger portion of the surface, and almost universally 
of an exactly circular or cup-shaped form, fore- 
shortened, however, into ellipses towards the limb; 
but the larger have for the most part flat bottoms 
within, from which rises centrally a small, steep, 
conical hill. They offer, in short, in its highest 
perfection, the true volcanic character, as it may be 
seen in the crater of Vesuvius. And in some of 
the principal ones, decisive marks of volcanic stra- 
tification, arising from successive deposites of eject- 
ed matter, may be clearly traced with powerful 
telescopes. What is, moreover, extremely singular 
in the geology of the moon, is, that although nothing 
having the character of seas can be traced, (for the 
dusky spots which are commonly called seas, when 
closely examined, present appearances incompati- 
ble with the supposition of deep water,) yet there 



imjnTf'ff'T*^'-^"*'"'"'^'"'- 



WONDERS OF THE HEAVENS 



123 



are large regions perfectly level, and apparently of 
a decided alluvial character. 

It is in consequence of the mutual gravitation of 
all the several parts of matter, which the Newtonian 
law supposes, that the earth and moon, while in 
the act of revolving, monthly, in their mutual orbits 
about their common centre of gravity, yet continue 
to circulate, without parting company, in a greater 
annual orbit round the sun. We may conceive 
this motion by connecting two unequal balls by a 
stick, which, at their centre of gravity, is tied by a 
long string, and whirled round. Their joint systems 
will circulate as one body about the common centre 
to which the string is attached, while yet they may 
go on circulating round each other in subordinate 
gyrations, as if the stick were quite free from any 
such tie, and merely hurled through the air. If 
the earth alone, and not the moon, gravitated to 
the sun, it would be dragged away, and leave the 
moon behind, and vice versa ; but, acting on both, 
they continue together under its attraction, just as 
the loose parts of the earth's surface continue to 
rest upon it. It is, then, in strictness, not the 
earth or the moon which describes an ellipse around 
the sun, but their common centre of gravity. The 
effect is to produce a small, but very perceptible, 
monthly equation in the sun's apparent motion as 
seen from the earth, which is always taken into 
account in calculating the sun's place. 

And here, i. e. in the attraction of the sun, we 
have the key .to all those differences from an exact 
elliptic movement of the moon in her monthly 
orbit, which we have already noticed, viz. to the 
retrograde revolution of her nodes ; to the direct 
circulation of the axis of her ellipse ; and to all her 
other deviations from the laws of elliptic motion. 
If the moon simply revolved about the earth under 
the influence of its gravity, none of these pheno- 
mena would take place. Its orbit would be a per- 
fect ellipse, returning into itself, and always lying 
in one and the same plane : that it is not so, is a 
proof that some cause disturbs it, and interferes 
with the earth's attraction; and this cause is no 
other than the sun's attraction — or, rather, that 
part of it which is not equally exerted on the earth. 



Suppose two stones, side by side, or otherwise 
situated with respect to each other, to be let fall 
together ; then, as gravity accelerates them equally, 
they will retain their relative positions, and fall 
together, as if they formed one mass. But suppose 
gravity to be rather more intensely exerted on one 
than the other; then would that one be rather 
more accelerated in its fall, and would gradually 
leave the other ; and thus a relative motion between 
them would arise from the difference of action, 
however slight. 

The sun is about 400 times more remote than 
the moon; and, in consequence, while the moon 
describes her monthly orbit round the earth, her 
distance from the sun is alternately 4ffTrth part 
greater and as much less than the earth's. Small 
as this is, it is yet sufficient to produce a percepti- 
ble excess of attractive tendency of the moon 
towards the sun, above that of the earth when in 






the nearer point of her orbit, M, and a correspond- 
ing defect on the opposite part, N ; and, in the 
intermediate positions, not only will a difference of 
forces subsist, but a difference of directions also; 
since, however small the lunar orbit, M N, it is not 
a point, and, therefore, the lines drawn from the 
sun, S, to its several parts cannot be regarded as 
strictly parallel. If, as we have already seen, the 
force of the sun were equally exerted, and in 
parallel directions on both, no disturbance of their 
relative situations would take place ; but from the 
non-verification of these conditions arises a disturb- 
ing force, oblique to the line joining the moon and 
earth, which in some situations acts to accelerate, in 
others to retard, her elliptic orbitual motion; in 
some to draw the earth from the moon, in others 
the moon from the earth. Again, the lunar orbit, 
though very nearly, is yet not quite coincident with 
the plane of the ecliptic ; and hence the action of 
the sun, which is very nearly parallel to the last- 
mentioned plane, tends to draw her somewhat out 
of the plane of her orbit, producing the revolution 
of her nod,es, and other phenomena less striking. 



124 



WONDERS OF THE HEAVENS. 



SECTION II. 

Phases of the moon — Law of their variation — The new holding the 
old moon — Earthshine — Earth new when the moon is old, and vice 
versa — Proportion of moonlight at different seasons and places — 
Harvest-moon ^Libration in latitude — In longitude — Diurnal — Lu- 
nar mountains — Atmosphere. 

The period of time during which the appearances 
now in question succeed each other, is the synodic 
revolution of the moon, or, as it is commonly called, 
a lunar month. There is a certain period during 
which the moon is not at all visible ; and in the 
course of which, as we know from observation and 
computation of her course, she has the same right 
ascension with the sun, or comes to the meridian 
at the same time with him. It is some time after 
this before she becomes visible, and when she does 
so, she is seen in the west soon after sunset, with 
the appearance of a very thin crescent, the bright 
and visible part having the side nearest to the sun 
convex towards him, and apparently semicircular ; 
the inner part, or the part farther from the sun, 
being elliptical, and convex in the same direction 
with the outer. From this time, as the moon's 
motion eastward in the heavens is greater than the 
sun's, in the ratio of thirteen to one nearly, their dis- 
tance from each other continually increases, as the 
moon comes to the meridian continually at a longer 
interval after the sun ; and while she does so, the 
breadth of the crescent continually increases, the 
outward or western line continuing to be circular, 
but the inner ellipse continually becoming less 
strongly curved, until, when the moon is distant 
about ninety degrees from the sun, and comes upon 
the meridian about six hours after him, this inner 
curve is changed into a straight line, and the 
appearance is that known by the name oi]iaJf-7noon. 
After this time the line becomes again elliptical, 
but has its convexity towards the side most distant 
from the sun, or bulges out in that direction, and 
the two lines which appear to bound the moon be- 
come concave to each other. In this condition the 
moon is called gibbous, and the side of the moon 
most distant from the sun continually becomes more 
and more strongly curved, and the apparent 
breadth of the moon consequently greater, until. 



when the right ascension of the moon is one hun- 
dred and eighty degrees different from that of the 
sun, and she comes to the meridian twelve hours 
after him, or at midnight, this side of the moon, as 
well as the other, is a semicircle ; and the moon 
appears completely round in the heavens, or, as 
we say, it is full moon. From this period, although 
the moon still comes upon the meridian longer and 
longer after the sun, she approaches him in dis- 
tance, for no points upon the sphere can be distant 
from each other more than one hundred and eighty 
degrees ; and when the difference of right ascen- 
sion, in the direction in which it is measured, ex- 
ceeds this quantity, the distance measured backward 
must fall short of it : thus, if the moon comes to 
the meridian fifteen hours after the sun, or the 
difference of their right ascension is two hundred 
and twenty-five degrees, the distance between 
them, measured in the opposite direction, is only 
nine hours, or one hundred and thirty-five degrees, 
or she comes on the meridian only nine hours be- 
fore the succeeding noon. After the full moon, 
therefore, the distance begins to diminish, and as 
it diminishes it is found that the appearances visible 
during its increase succeed each other in the con- 
trary order; that the moon becomes gibbous, and 
her apparent breadth continually diminishes, the 
side now next the sun continuing apparently circu- 
lar, the other becoming elliptical, and continually 
less and less strongly curved, until, about the time 
when the distance between them is two hundred 
and seventy degrees in one direction, or ninety 
degrees in the other, the appearance of half-moon 
is again presented ; and from that time forward the 
moon appears as a crescent, continually diminishing 
in breadth, until, at length, when she has arrived as 
near the sun as she was when she first became 
visible at the beginning of the month, she disap- 
pears, and is not again seen till the corresponding 
period of the next month, when the same order of 
appearances recommences. The appearances dur- 
ing the period of her diminution are exactly the 
same with those during the period of her increase, 
and correspond to exactly the same distances in 
each case. Thus, if the shape of the moon be 



mv*»amw sEas 



WONDERS OF THE HEAVENS 



125 



observed when her angular distance from the sun 
is seventy degrees east, it is found that she has 
exactly the same shape when two hundred and 
ninety degrees east, or seventy degrees west of 
him : the only difference is, that the circular part, 
or limb, of the moon, which was turned in the 
former case towards the west, is turned in the 
latter towards the east. 

It is obvious, therefore, that these appearances, 
or phases, as they are called, of the moon, depend 
upon her angular distance from the sun, for they 
continually vary with the variation of that quantity ; 
the visible magnitude of the moon increasing when 
that quantity increases, and diminishing when it 
diminishes ; and, when that quantity is equal at 
different periods, these visible magnitudes being 
equal also. Nor is it difficult to perceive that the 
appearances presented correspond to those which 
would obtain, if the moon were an opaque body, 
giving forth no light of its own, but capable of re- 
flecting the light received from the sun. 

It is evident that the moon is not luminous of 
herself, for if she were she would always be visible 
when above the horizon, whatever were her posi- 
tion with respect to the sun. Considering her, 
therefore, as opaque, but capable of reflecting light, 
it is plain that one portion of the moon would 
always be light, namely, the whole portion which 
is turned towards the sun, and the rest would be 
dark. We should consequently see only that por- 
tion which the sun illuminated, and only so much 
of that portion as was on the side of the moon 
turned towards us. When therefore the moon was 
between us and the sun, she would be invisible, 
because the whole of her enlightened side would be 
turned from us; gradually, as she receded from 
this position, some part of her enlightened side 
would be within the view of an observer at the 
earth, and this part would continually increase as 
she got farther from the sun, until, at length, when 
she was upon the opposite side of the earth, or the 
earth was between her and the sun, the same por- 
tion of the moon would be turned towards the sun 
and earth, or the whole of the enlightened portion 
would be visible to us. From this time she would 



again approach the sun, and some part of the en- 
lightened portion would continually disappear ; and 
as the quantity visible would depend merely on the 
relative positions of the sun, moon, and earth, the 
decrease would follow the same law as the increase, 
although in a reversed order, for the relative posi- 
tions would succeed each other in this manner. 
These conclusions may be illustrated by a figure. 




Let T represent the earth, S the sun, (of which, 
however, the distance must be taken to be very 
great, although it is not represented so for the con- 
venience of the figure,) and A, B, C, D, E, &c., 
different positions of the moon (which we will sup- 
pose spherical) in her orbit. The enlightened por- 
tions of those circles will represent the enlightened 
part of the moon in each case ; and, as the part of 
the moon turned towards the earth will be that, or 
very nearly that, within the circle passing through 
A, B, C, &c., the part visible in each case will be 
only so much of the enlightened part as is within 
that circle. The figures in the outer circle, a, b, c, 
&,c., will represent the appearances, or phases, of 
the moon in the corresponding situations, the light 
parts only being visible. Thus, at A, the whole of 
the enlightened part of the moon is turned from the 
earth, and none of it, in consequence, is visible; 
at B and H, a small part only, and that equal in 
both instances, is visible, namely, the light parts 
within the circle; and the appearances presented 
are represented by b and h, two similar figures, 
but with the convexity of the light part turned, in 
each case, towards S, and consequently in different 
directions with respect to T. To explain fully 
the correctness of the representation, the figures 
b, c, &.C., should be considered as if they were per- 



126 



WONDERS OF THE HEAVENS 



pendicular to the plane of the paper. The circle 
drawn through A, B, &c., will very nearly repre- 
sent the line bounding the part of the moon visible 
fi-om the earth; and this will be a circle described 
on the sphere very nearly perpendicular to the 
plane of the moon's orbit, and to the line joining 
the earth and moon, or the moon's radius vector ; 
it wilL therefore be seen as a circle perpendicular 
to that same plane, or as the outer line of the 
light part of Z>. The dark line also, the boundary 
of the enlightened part of the moon visible from 
the earth, will also be a circle of the sphere, 
but this will be seen obliquely from the earth, 
and will therefore assume an oval appearance; it 
therefore will be represented by the inner bounda- 
ry of the light part of b. These lines will evi- 
dently meet in a point, as they do in the figure, 
because the corresponding circles in B do actually 
meet so, and the visible light part of the moon it- 
self consequently terminates in one. 

-The reader will have no difficulty in ascertaining, 
in the same manner, the correctness of the other 
delineations. We conclude therefore that the moon 
shines by light reflected fi-om the sun ; and we 
shall find a still farther proof of it when we treat 
of eclipses, for we shall see that even when she is 
opposite to the sun, at the time of the full moon, if 
the earth is directly between her and the sun, so 
as to intercept his light entirely, she then also be- 
comes invisible. 

The law which determines the proportion of the 
surface of a spherical heavenly body, (depending 
for its light on the reflection of light from the sun,) 
visible at different times, according to its different 
situations with respect to the sun, may be investi- 
gated without any difficulty by a reader very slightly 
acquainted with mathematics ; and it is of the more 
importance to do so, because we shall not only 
find that it accounts for the various phases of the 
moon, but that it serves to explain the appear- 
ances of other heavenly bodies. We proceed, 
therefore, to investigate it. We confine ourselves 
to the case of a spherical heavenly body, because 
all those to which we shall have to apply our 
results are very nearly of that form. 



If the moon, or any other body which receives 
the sun's rays, be spherical, the boundary of the 
part on which they fall, or of the enlightened part, 
will necessarily be circular. This follows immedi- 




ately from a very simple consideration. Let A 
represent the centre of any opaque sphere whatso- 
ever, and B a luminous object shining upon it; and 
let the line A B be drawn joining A and B, and 
passing through the sphere at D ; and let B C be a 
tangent to the sphere. It is evident that C will be 
a point in the boundary of the illuminated part of 
the sphere, for no point farther from B than C is, 
can receive a ray of light from B, as some part of 
the opaque sphere will be between them ; and 
every point between C and D must receive such 
rays, for there is nothing to interpose and prevent 
them from arriving there. 

Now, all tangents drawn to a sphere from the 
same point are equal to each other. At every point 
therefore in the boundary of the illuminated part 
the value of C B is the same ; A C, the radius of 
the spherical body, is equal at all points, and A B 
is always the same line; the value of the angle 
D A C is the same in the case of every point in this 
boundary. Every point then in this boundary is at 
the same angular distance from the point B, or 
from D, and therefore in the circumference of a 
circle whose pole is D, and consequently whose 
plane is perpendicular to the line A B. 

The result will require to be a little modified, as 
light actually proceeds from every part of a very 
large body, namely, the sun. If the sun were of the 
same size as the moon, the extreme rays would be 
parallel ; if smaller, they would continually diverge 
from each other ; if larger, they would converge to 
a point. These results are obvious in themselves ; 
or they will immediately appear by the inspection 
of the plate, where, if S represents the sun, and 
A, B, C, three bodies, the first equal to the sun in 
size, the second larger, the third smaller, the ex- 
tremities of the shaded figures beyond them will 



WONDERS OF THE HEAVENS 



127 



evidently represent the course of the extreme rays, 
and the figures themselves the shadows cast by the 




bodies, which, in the two former cases, would be 
prolonged to an infinite distance ; in the latter, they 
would terminate as in the figure. The third case 
represents that of the moon, which is smaller than 
the sun ; the boundary of the illuminated part there- 
fore will be determined by rays, not diverging from 
the illuminating body S, but converging to a point 
on the other side of the moon. But still, as they 
all met in a point, the boundary of the illuminated 
part will be a circle, in the same manner as before ; 
and as the difference of the diameters of the sun 
and moon is small in comparison with their distance, 
the rays will converge very slowly, and the extre- 
mity of the shadow, the point to which the extreme 
rays converge, will be very distant from the moon; 
and the boundary therefore, in this case also, will 
differ very little from a great circle. The whole 
part illuminated therefore rather exceeds half the 
sphere, but by so small a quantity, that we may 
say generally that half of any spherical heavenly 
body is illuminated by the sun, and that the boun- 
dary of the illuminated part is a great circle of the 
sphere, whose plane is perpendicular to the line 
joining the centre of the body with the centre of 
the sun. 

Again, (in the last figure but one,) if we suppose 
B, instead of being the position of the luminous 
body, to be the position of an observer looking at 
the spherical body A, he will evidently see all be- 
tween D and C, and nothing beyond C. C then 
will represent a point in the boundary of the part 
of the sphere visible to the observer, and, by the 



same reasoning as before, this boundary must be 
circular, and its plane perpendicular to A B ; and 
it may be considered as a great circle of the 
sphere. 

The boundary of the part turned toward the 
earth, and that of the enlightened part of the moon, 
are each of them great circles, and therefore bisect 
each other ; or, the visible boundary is a complete 
semicircle. Whenever, therefore, the moon is visi- 
ble, her cusps, or extreme points, are at the extremi- 
ties of the diameter, and during all her phases 
(however small be the part of her surface visible to 
us) we may make observations of her apparent 
diameter for ascertaining her distance and the 
form of her orbit. 

When the moon is in conjunction with the sun, i. e. 
between the sun and earth, the line joining the 
earth and moon is in the same direction as that 
joining the moon and sun. When the moon is in 
opposition, i. e. has the earth between her and the 
sun, the line joining the earth and moon is in the 
opposite direction from that joining the earth and 
sun, or they are the same lines prolonged, thus 
making an angle of one hundred and eighty degrees 
with each other. The whole face of the moon is 
therefore visible. When the moon is in quadrature, 
these lines make a right angle, and only one half 
of the moon's illuminated face is visible to the in- 
habitants of the earth. 

It is perhaps necessary to observe, that, when 
we speak of the moon as reflecting light from the 
sun, we do not mean that she reflects it so as to 
present an image of the sun on one point of her 
surface, like a mirror; but that the light gets 
broken and diffused from part to part of her surface, 
and finally sent forward to us in such a manner as 
to render the whole surface of the enlightened part 
visible ; just as light is diffused over bodies on the 
earth, which, if perfectly smooth would only form 
an image of the sun, but do actually show by re- 
flected and broken light, the whole of their own 
surface, its form and color. 

It is evident, from the law of variation which we 
have deduced, that almost immediately after the 
moon and sun cease to be in the same line, there is 



KinsmiaMssamz 



«.mm»tif.i.ni»»a>J»» 



128 



WONDERS OF THE HEAVENS 



some portion of the illuminated part of the moon 
turned towards the earth. Yet it is some time be- 
fore its magnitude becomes considerable. During 
this period also the moon is apparently near the 
sun, and consequently in a very light part of the 
heavens ; and it is therefore a good while before she 
really becomes visible, for she cannot be seen till 
the light which she reflects is sufficient to be dis- 
tinguished from that which the sun spreads gene- 
rally over the region of the atmosphere through 
which the rays that proceed from her must pass. 
The length of time, therefore, during which she is 
not actually seen, furnishes no exception to the 
correctness of our results. 

There is a remarkable appearance presented by 
the moon when the visible part, according to the 
principles we have established, would be small, 
which this is the proper season for explaining. At 
these periods the whole of the moon's disc is fre- 
quently seen, part bright, and having its magnitude 
the same with that which we have explained as ihe 
whole visible magnitude of the moon ; the rest visi- 
ble by a pale and delicate light, and appearing, 
from the ordinary effect of brightness in augment- 
ing the apparent magnitude of objects, somewhat 
smaller in its dimensions than the brighter part. 
The appearance thus described, from its being 
much more frequently observed in the evening, soon 
after the moon's first appearance, or after the new 
moon, when more persons have the opportunity of 
seeing it than in the early morning, preceding the 
disappearance of the moon at the latter end of the 
month, has received, in common speech, the odd 
name of '■'■the old moon in the new moon's arms.'' The 
French, with more accuracy of expression, have 
named it, from the pale color of the greater part 
of the moon, lumiere cendree, or ashy light. The 
cause of this light is obvious : the earth, as well as 
the moon, reflects light, and, consequently, the en- 
lightened part of the earth, or so much of it as is 
turned towards the moon, will reflect light to that 
body. Some of that light will again be reflected 
back to the earth ; and thus even that part of the 
moon which receives no light directly from the sun, 
may, by indirectly receiving it from the earth, be- 



come, as we see it, faintly visible. The appear- 
ance, thus occasioned, has received the name 
of earthshine. The light indirectly supplied must 
necessarily be far inferior in quantity and brightness 
to that which the directly enlightened part of the 
moon receives immediately from the sun ; and thus 
the great inequality of brightness in the two visible 
portions is accounted for. The only apparent 
difficulty arises from the circumstance that the ap- 
pearance in question is only seen when the directly 
illuminated part is small. In reality, however, this 
seeming difficulty confirms the explanation given, 
for there are two obvious reasons for it. As the 
directly-illuminated part increases, its light becomes 
greater, and the light diffused over that part of the 
atmosphere through which the moon shines greater 
also : a stronger light therefore is required to be 
distinguishable. But this is not all ; the light actu- 
ally supplied to the moon from the earth diminishes. 
The earth being a spherical body, and reflecting 
light, appearances or phases will be presented by 
the earth to the moon similar to those which we, 
on the earth, observe in the moon; and all our re- 
sults will be true for this case, as well as for that 
already examined. The order indeed will be dif- 
ferent. Thus, when the moon is invisible to us, 
being between the earth and sun, the earth will 
turn the same part to the sun and moon, and will 
be visible to the moon with a full face ; when we 
see the full moon, the earth is between the moon 
and sun, and therefore invisible to the moon. The 
part of the earth visible from the moon diminishes 
as the visible part of the moon increases, and of 
course the quantity of light which the earth reflects 
to the moon diminishes also. The power therefore 
of distinguishing the moon by this light reflected 
from the earth, is diminished as the part visible by 
light directly reflected from the sun is increased; 
both because less light is thus transmitted to the 
moon, and because more is required before it can 
be distinguished. 

We have thus explained the manner in which the 
proportion of the moon which is visible at different 
periods of the month varies. This proportion, how- 
ever, is not the only thing which we can observe 






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WONDERS OF THE HEAVENS. 



with respect to her. Many singular marks and 
spots are apparent upon her, from which various 
and important conclusions may be drawn. But be- 
fore we proceed to state these observations, and 
draw from them the inferences to which they lead, 
it will be worth while to pause, and deduce from 
the results already obtained some remarkable con- 
sequences, which materially tend to the conven- 
ience of mankind. 

The most obvious practical service of the moon, 
as far as mankind are concerned, is the supply of 
light which she affords, during the otherwise dark 
hours, while the sun is below the horizon. But she 
herself is sometimes above, sometimes below, the 
horizon ; and as her declination is continually vary- 
ing, her periods of continuance above the horizon 
continually vary also. Her light also is different 
at different periods of her course, — sometimes none, 
sometimes little, and therefore of little practical 
utility ; generally however enough to be of material 
service to the sailor, the traveller, and even to the 
husbandman ; and this most when her light is the 
brightest, or at the full moon. It therefore matters 
little to man whether she is above or below the 
horizon at night, as long as her own light is little 
or nothing ; but it is of much importance that she 
should be above the horizon at night, when her light 
is considerable. Now this, by the conditions of her 
motion, she necessarily is. The quantity of light 
which she reflects is greatest when her distance 
from the sun is greatest, or when the difference of 
their right ascensions is one hundred and eighty 
degrees, or the time between their appearances on 
the meridian is twelve hours. When the moon's 
light is greatest, therefore, she is on the meridian at 
midnight ; and as her light is always greater as her 
distance from the sun, and consequently as the in- 
terval of time between their appearance on the 
meridian, is greater, the periods of her greater 
light will always bring her on the meridian nearer 
midnight than those of her less brilliancy; and, 
therefore, taking the whole course of one of her 
revolutions, she will be above the horizon during 
a larger proportion of the night, as her light, and 

consequently her power of being useful, are greater. 
17 



The nights, however, are of different lengths at 
different periods of the year; and, consequently, if 
the moon, when at her greatest brightness, were 
always at the same declination, and thus had the 
same proportion of her diurnal course above the 
horizon in all these cases, she would supply light 
through a much smaller proportion of the long and 
dark nights of winter, than of the short and com- 
paratively light nights of summer. But this is not 
the case. For the purpose of illustration, we will 
suppose the moon to move in the plane of the 
ecliptic, and, as usual, that the north pole is above 
the horizon. The full moon takes place when the 
difference of longitude of the sun and moon is one 
hundred and eighty degrees. Taking, then, the 
extreme cases of the two solstices, it is evident that 
when the sun is at the summer solstice, or in the 
tropic of Cancer, the full moon, being one hundred 
and eighty degrees distant, would be in the tropic 
of Capricorn ; the sun therefore being at his greatest 
north declination, the moon would be at her greatest 
south declination : and throughout all that half of 
her orbit which is most distant from the sun, and 
where consequently her light is greatest, and more 
than half her face visible, her declination would be 
south. In this case, then, when the sun having his 
greatest north declination the day is longest, the 
moon would have her greatest south declination, 
and be least time above the horizon, when at the 
full: and during the whole time that more than 
half her face is visible, her declination would be 
south, and less than half of her diurnal course 
would be above the horizon. Exactly the contrary 
results would evidently follow when the sun is in 
the tropic of Capricorn, when he has his greatest 
south declination, or the days are shortest. In this 
case, the moon would be at the full when in the 
tropic of Cancer, or at her greatest north declina- 
tion ; and throughout all that half of her orbit most 
remote from the sun, and when more than half her 
face is visible, her declination would be north ; and 
consequently, during this whole period, she would 
be more than half her time above the horizon, and 
longest of all when her light is the greatest. In 
intermediate positions of the sun, the results would 



criiBMw: u«.t:w:#=n>w«mmi*.t> 



130 



WONDERS OF THE HEAVENS. 



be intermediate ; but it is not necessary to enter 
into any detail of them. The reader will have no 
difficulty in pursuing, if he is inclined, a similar 
course of argument with respect to them. 

Again, the greater the elevation of the pole above 
the horizon, the greater is the inequality of day 
and night, and the longer does a body with north 
declination continue above, or a body with south 
declination continue below, the horizon. The more 
elevated the pole, therefore, the longer is the moon 
above the horizon when her declination is north; 
and as, during the winter, her declination is north 
while her light is greatest, the proportion of time 
during which she continues above the horizon while 
her light is greatest increases, at that season, as the 
latitude increases, or as the nights themselves are 
longer. Taking the extreme case, where the pole 
is in the zenith, the moon will never set while her 
declination is north; and at the winter solstice it 
will be so during the whole time that more than 
half her face is visible. There will, therefore, be a 
fortnight of the brightest moonlight at that season 
when the night, from the complete absence of twi- 
light, would otherwise be darkest. There will 
always be a fortnight at a time there, during which 
the moon will be above the horizon; but as the 
sun approaches the equinox, the light given by the 
moon during part of this fortnight will diminish. 
At this time, however, it may better be spared, for 
by this time, though the sun does not appear on 
the horizon, there will be a considerable twilight. 

It is abundantly plain that the same conse- 
quences will follow from south declination where 
the south pole is above the horizon, as we have 
seen to follow from north declination where the 
north pole is so ; and thus that this beneficent pro- 
vision, by which the greatest quantity of moonlight 
is afforded to those regions, and at those seasons, in 
which it is most wanted, is general over the whole 
earth. 

The moon however moves not in the plane of the 
ecliptic, but in one inclined to it at an angle of a 
little more than five degrees ; but this difference 
will not materially affect the results we have ob- 
tained. It will, indeed, at different times, according 



to the place of the. nodes of the moon's orbit, very 
materially affect the actual length of time during 
which she is above the horizon ; but she never can 
be distant much more than five degrees from the 
ecliptic, and so much only during a very small por- 
tion of her course. The ecliptic itself is, at its 
greatest distance, more than twenty-three degrees 
from the equator. The distance of the moon from 
the ecliptic, therefore, being so much smaller, can- 
not, except for a very small space comparatively, 
vary the nature of our results, (though it will their 
amount,) or make that declination north which 
would otherwise be south, or the contrary. It 
cannot even materially alter the point at which the 
declination would be greatest, though it may make 
that greatest declination differ, in different cases, 
by upwards of ten degrees. Thus, if we suppose 
the nodes of the moon's orbit to coincide with the 
equinoxes, the moon, when ninety degrees from 
the node, will be about five degrees north or south 
of the ecliptic at the tropic of Cancer, as the part 
of her orbit between the vernal and autumnal 
equinox is that which lies above or below the plane 
of the sun's orbit. Her declination at this point, 
therefore, in the one case will be about 28° 30' north, 
in the other only 18° 30' north; but in each case 
it will be the greatest north declination which, 
during that revolution, she attains. When, however, 
the node is not at the equinox and solstice, this 
will not necessarily be the case ; but it can never 
differ much from it. We may therefore conclude 
our results to be generally true ; and we thus see 
that the shape and motions of the moon, and the 
manner in which she reflects light to the earth, are 
so ordained as to make her most serviceable when- 
ever and wherever her services are most wanted, — 
an incidental consequence, indeed, of the general 
laws governing her motion, but one of the many 
remarkable instances in which, throughout the ap- 
pearances of nature, we see, not only that the 
general scope and tendency of her operations are 
beneficial, but that collateral benefits continually 
flow from the manner in which those operations are 
conducted. 

Another application of the same principles of 



WONDERS OF THE HEAVENS 



131 



reasoning, and, although in an inferior degree, a 
similar instance of a beneficial result arising inci- 
dentally from the operation of the general laws 
established in nature, will be found in the explana- 
tion of the phenomenon known by the name of the 
harvest moon. Whether we consider the moon as 
moving in the plane of the ecliptic, or in that of 
its real orbit, the variation of its declination will be 
most rapid where its orbit cuts the equator; and 
as no part of the real orbit is much more than five 
degrees distant from the ecliptic, its intersection 
\vith the equator cannot be far distant from the 
intersection of the ecliptic with the equator. The 
moon therefore moves most rapidly northward when 
near the equator, and also near the first point of 
Aries; most rapidly southward when near the 
equator and the first point of Libra. 

When the sun is near one equinoctial point, the 
moon, when full, is near the other, and necessarily 
near the equator also. The difference of their right 
ascension, estimated in time, is twelve hours, and 
this is also the length of the day at that period. 
The moon therefore will rise in the east, just as 
the sun sets in the west. As the moon completes 
her revolution round the earth in a little less than 
twenty-eight days, her motion, if uniform, would 
be at the rate of about thirteen degrees a day ; or, 
omitting any consideration of the manner in which 
the obliquity of her orbit would affect the results, 
she would come to the meridian of the place about 
fifty-two minutes later on each successive day. If, 
therefore, her declination continued the same, as 
she would always be an equal time above the hori- 
zon, she would rise and set about fifty-two minutes 
later every day; but when she is near the first 
point of Aries, her declination, and consequently 
the period during which she is above the horizon, 
rapidly increases ; and consequently she is longer 
above the horizon before reaching the meridian, 
and the time of her rising is not retarded nearly to 
this average amount of fifty-two minutes. The 
time by which her setting is retarded is increased 
by as great a quantity as that by which the re- 
tardation of her rising is diminished. The degree 
of effect thus produced, differs in different regions 



of the earth : here it is such that for two or three 
days the moon's rising is nearly as much accelerat- 
ed by her motion northward, as it is retarded by 
the continually later period at which she comes to 
the meridian: the consequence, therefore, is, that 
she appears during this time to rise at very nearly 
the same hour, that is to say, almost at the instant 
of sunset. Bright moonlight, therefore, (when the 
moon is full near Aries, or the sun is near Libra,) 
for two or three days immediately succeeds the 
disappearance of the sun ; and as, by the general 
course of the seasons, this period is about the be- 
ginning of autumn, or the close of harvest-time, 
when the opportunity thus afforded of carrying on 
the works of husbandry after sunset is often very 
valuable, we speak, in common language, of the 
harvest moon, when we speak of her as rising at that 
season successively for two or three nights nearly 
at the same time. 

About the vernal equinox, exactly a reverse 
operation must take place. The moon when full 
is then near the equator, but moving southward, 
and her change of declination from day to day is 
the greatest. Her appearance on the meridian 
still continues to be later from day to day ; but as 
her periods of being above the horizon diminish, 
her rising and setting will each be brought nearer 
to the time of her being on the meridian, and her 
rising is therefore additionally retarded, but the 
time of her setting is accelerated. Instead, there- 
fore, of setting every day considerably later, her 
settings at this period are nearly at the same time 
for two or three days near the full moon ; and for 
the same reason as before, her setting must, at the 
full moon, be just when the sun rises. For two or 
three days, therefore, at this period, the moon sets 
just about sunrise. The result is of no practical 
importance here ; but it furnishes another instance 
of the application of the same principle, and is 
therefore inserted to familiarize the reader with it. 
Besides, although unimportant in this hemisphere, 
the inhabitants of the southern half of the world, 
who have their autumn at the time of our spring, 
are thus furnished, in their turn, with the advantage 
of a harvest moon. Of course, in every revolution 



L HJW.» 4 uui i — n j^ t. mnm 



132 



WONDERS OF THE HEAVENS 



of the moon there are periods when her rising and 
setting are thus affected, for they must be so when- 
ever her orbit crosses the equator ; but they excite 
little observation in other instances, not being then 
connected with the close or the beginning of day. 

Every one is aware that the moon does not pre- 
sent (as the sun does, at least to the naked eye,) a 
uniform face of uninterrupted light, but that she 
appears checkered and diversified with darkish spots 
and lines: indeed, these have been so constantly 
the subject of observation, that, in most countries, 
fanciful resemblances have been imagined for them ; 
and we still hear of the man in the moon, his bush, 
and his dog. The probable cause of these appear- 
ances will be matter of consideration hereafter ; 
but independently of any such sp'eculations, they 
at once furnish us with the means of ascertainina; a 
curious and important fact with respect to the 
motions of the moon. 

As we have the means of making these observa- 
tions upon the surface of the moon, we can tell by 
them what part of her surface is turned towards us. 
If these appearances are from time to time different, 
it would be natural to conclude that different parts 
of the moon are at different periods presented to 
us : if they are always the same, the same part of 
the moon is always turned towards us, unless, in- 
deed, all her parts are marked so exactly alike that 
the one would be indistinguishable from the other. 
This, however, is not the case; for we see, at the 
period of full moon, half, or very near half, the 
surface of the moon, and the marks and spots with 
which it is diversified ; and these, when examined 
through a telescope, are so different in their 
character, that any alteration in their positions Vv^ith 
respect to us would be immediately detected. 
We are thus able by observation to ascertain what 
part of the moon's face is presented to us; and we 
are so, whether the full moon or any smaller por- 
tion of her disc be presented to us, because, if we 
once learn to distinguish the marks upon her sur- 
face, and any of these be upon the part which is 
actually visible to us, we see what part of her disc 
that is, and consequently in what manner she is 
placed with respect to us. 



The result of these observations is, that very 
nearly the same part of the moon is always turned 
towards us. There are some slight differences in the 
appearances presented at different periods of the 
month, but they are so small that, for the present, 
they may be left out of our consideration. Hence 
we may easily ascertain that the moon must herself 
have a motion of rotation, and that the period of 
her rotation must be the same as that of her revolu- 
tion round the earth. Referring again to the figure 
on page 125, we may take the figures in the inner 
circle to represent different positions of the moon : 
and the shaded part of the figure. A, will represent 
the half turned to the earth in that position ; the 
white part, the part turned from it. As, in the 
figure, the boundaries of the white and shaded part 
in the figures of the inner circle are parallel in each 
case, the shaded part may, in every case, represent 
the side of the moon which was turned to the earth 
at A, if we suppose that the moon has no motion 
of rotation. The part of the moon actually turned 
towards the earth will, in each case, be very nearly 
represented by the part within the circle joining 
A, B, C, &c. It is obvious, therefore, from inspec- 
tion of the figure, that, if the moon has no motion of 
rotation, a different part of her surface will be pre- 
sented to the earth in every diflFerent position. 
Thus, at A she presents one side to the sun, the 
opposite side to the earth ; at E she would present 
the same side, which she before presented to the 
sun, to the earth also ; and in the intermediate po- 
sitions, B, C, D, she would continually turn towards 
the earth less and less of the part turned towards 
it at A, as the positions B, C, D, themselves suc- 
cessively became more distant from A. We find, 
however, that this is not the case, but that at every 
position very nearly the same part of her surface is 
turned towards the earth. This can only be done 
in one way. If the same part of the moon is to be 
turned towards the earth at B which was so at A, 
or the shaded part in the figure is to coincide with 
the part within the connecting circle, it can only 
do so by a turning of the moon in the same direc- 
tion, so as to bring it into the required position ; 
and in the same manner the moon must have turned 



WONDERS OF THE HEAVENS 



133 



yet further to produce the same effect at a greater 
distance, as C, or D, and must have turned half 
round to make the same side face the earth at 
E, one extremity of the diameter A E, which had 
done so at A, the other. The same motion must 
evidently continue beyond E; and that the same 
part of the moon may again be presented to the 
earth on her return to A, the revolution must be 
completed at her return to A, and not sooner. 
There is, then, a revolution of the body of the moon, 
and it is completed during the space of a periodic 
month ; for it is obvious that the position of the sun 
has nothing to do with the part of the moon which is 
really turned towards the earth, though it deter- 
mines that which is visible, and consequently that 
the time of rotation is the same with that of the 
moon's return to the point A, not as a point situated 
between the earth and the sun, but as a point in a 
given direction from the earth ; or, in other words, 
that it is the same with the length of the periodic, 
not of the synodic, revolution. 

In the figure, as drawn, the moon is merely 
represented by a circle drawn on the plane of the 
paper ; which obviously represents that of the 
moon's orbit, and the rotation deduced would be 
rotation in that plane, or round an axis perpendi- 
cular to that plane. If, however, the axis round 
which the moon turns is inclined at any angle to 
that plane, the appearances would be different. 
Let us call the extremity of the axis elevated above 
the plane of the paper, M, that depressed below it 
m; and let us suppose that, the axis is everywhere 
parallel to itself, and that, at the point A, the ex- 
tremity M is inclined a little towards the earth, 
and of course the extremity m a little away from it. 
It is plain that, on this supposition, an observer at 
the earth would have turned towards him a part of 
the moon a little beyond M, and that, towards the 
other side, he would not see quite so far as m. 
When the moon arrived at E, these appearances 
would be reversed ; the position of the axis con- 
tinuing parallel to itself, but its situation with re- 
spect to the earth being reversed ; the extremity m 
would now be inclined as much towards the earth, 
as, in the former position, M was; and as, in the 



former case, an observer would have had exposed to 
him parts beyond M, but not those extending to m, 
he would now have turned to him parts beyond 
m, but would not be able to observe those extend- 
ing to M. There would, therefore, be a sensible 
difference in the parts which he could observe 
under the two circumstances. It is plain, also, that 
there would be similar and corresponding changes of 
appearance in the intermediate situations. The facts 
actually observed, however, are found to correspond 
with the results deduced upon this supposition of a 
rotation on an axis moving parallel to itself, but not 
quite perpendicular to the plane of the moon's orbit. 
The points M, and m, are called (from their corre- 
spondence with the points called the poles of the 
earth,) the j5oZes of the moon; and the great circle 
perpendicular to the axis of the moon, is called, for 
a similar reason, the equator of the moon. The 
phenomenon which we have been explaining of the 
appearance of different parts of the moon's surface 
differently situated with respect to these poles, is 
called the moon's libration (rocking or balancing) 
in latitude. From the amount of this libration, 
the degree of inclination of the moon's axis to her 
orbit maybe ascertained: the angle is 84° 51' IV. 
This, however, is not all. The boundary of the 
part of the moon presented to the earth is a circle 
of the moon, the plane of which is perpendicular to 
the radius vector. The angle, therefore, which the 
positions of these planes will make with each other 
at different points of the orbit, will be equal to the 
angle made by the radii vectores at these points. 
The moon, however, moves in an ellipse, and con- 
sequently her angular velocity is not uniform : the 
angle traced by the radius vector, therefore, will not 
increase in the exact proportion of the time. If, 
then, the rotation of the moon be uniform, as well 
as complete in the periodic time of the moon, she 
will describe three hundred and sixty degrees on 
her axis in the same time that she takes to de- 
scribe three hundred and sixty degrees round the 
earth : but while she takes exactly half this time to 
describe one hundred and eighty degrees, a quarter 
of it to describe ninety degrees, and a tenth of it to 
describe thirty-six degrees, on her axis, in whatever 



irfcir""*'—— ""*"" 



134 



WONDERS OF THE HEAVENS 



part of her orbit this time be taken, she will not 
take accurately these same proportions of time to 
describe the corresponding angles of 180°, 90°, 
and 36°, around the earth in every part of her orbit. 
At some periods, therefore, when the moon's motion 
in her orbit is less than her mean motion, she will 
have turned further on her axis than is necessary 
to keep the same face directly turned towards the 
earth; at other times, when the moon's motion 
exceeds the mean motion, she will not have turned 
sufficiently far on her axis for that purpose; and 
the consequence would be, that in the former case 
some of the eastern side of the moon, in the latter 
some of the western, will be seen, beyond what was 
originally turned towards the spectator. The poles 
of the moon would be unaffected by the motion of 
rotation, and of course by its equality or inequality. 
These appearances, again, are actually found to 
take place, and are known by the name of the 
moon's libration in longitude. 

There is still another phenomenon of the same 
kind. The part of the moon presented to an ob- 
server at any place is bounded by a circle perpen- 
dicular to the line joining his place and the centre 
of the moon. To observers at different places, 
therefore, appearances in some degree different 
will be presented; for the moon is not so distant 
from the earth but that the lines joining her centre 
with different spots on the earth's surface may 
make a sensible angle, — in the extreme case not 
less than twice the horizontal parallax of the moon, 
or nearly two degrees on an average: and this 
angle will be that of the inclination of the planes 
bounding the part of the moon visible at each situa- 
tion. A similar consideration will explain a further 
variation of the appearances of the moon, which 
every day presents to us. When the moon rises in 
the east, an observer on the earth's surface will 
see a little more of her western and then upper 
side than he would do if placed in the centre of 
the earth; and when she is setting in the west, he 
will see a little more of her eastern and then 
upper side. This is called the diurnal, or paral- 
lactic, libration. 

A certain degree of variation in the appearances 



presented by the moon is thus shown necessarily to 
exist, on the supposition of her uniform rotation 
round a fixed axis; and the appearances which 
actually exist are found very nearly to correspond 
with that supposition. But in this, as in almost 
every astronomical result, we are obliged to qualify 
our first conclusions in order to arrive at complete 
correctness. We find that the appearances pre- 
sented so nearly correspond with those necessary 
on the supposition of uniform rotation round a fixed 
axis, that we are induced to conclude, in the first 
instance, that this supposition is strictly true; but 
more minute observation teaches us that it is not 
so. We have indeed no reason to doubt the 
uniformity of the motion of rotation ; but the posi- 
tion of the axis itself is found not to be invariably 
the same. It is always inclined at the same angle, 
or very nearly so, to the lunar orbit ; but its direc- 
tion is different, for it is always perpendicular to 
the line joining the nodes of the orbit; and as they 
make a complete revolution in 6793-42118 days, 
the axis of rotation of the moon will in that time 
go through all its positions with respect to the 
heavens. 

The moon continually turning the same face, or 
very nearly so, towards us, we are able to observe 
it, by the aid of powerful telescopes, with great 
accuracy. The consequence has been, that maps 
of that part of its surface which is exposed to us 
have been constructed, and that we have obtained 
considerable knowledge of its constitution, as well 
as of its motions. 

On looking at the moon through a powerful tele- 
scope, we observe very different degrees of bright- 
ness in different parts of the surface, and especially 
some bright spots, which have beyond them, in the 
direction opposite to that of the sun, a compara- 
tively dark shadow. The length and position of 
this shadow vary as the position of the spot with 
relation to the sun varies; the shadow being 
always opposite to the sun, but longer or shorter 
as the sun is more or less elevated above a plane 
touching the moon at that point, or the horizon of 
that point of the moon. It is obvious, from these 
appearances, that the dark part is really a shadow 







BSMSssttiMinni 



WONDERS OF THE HEAVENS 



135 



created by the interposition of the bright spot be- 
tween it and the sun, or that the bright spot is an 
elevation above the general level of that part of the 
moon where it stands, or a mountain in the moon. 

We are led to the same conclusion of the exist- 
ence of mountains in the moon by another remark- 
able appearance. The inner or oval edge of the 
moon is the boundary of light and darkness there. 
If the moon were perfectly smooth, this boundary, 
as we have seen, would be a perfect circle, and its 
appearance would be that of an accurate ellipse ; 
but if there are inequalities on the moon's surface, 
some of the higher points, beyond the line which 
would be the boundary of the visible part if smooth, 
would project into the light, and would be visible 
sometimes even while the depressed parts between 
them and the boundary would be in shadow. Thus, 
upon the earth's surface, the tops of mountains con- 
tinue to receive the light of the sun after he has 
set to the valleys or plains below them. Now 
these are exactly the appearances presented by the 
inner edge of the moon when seen through a tele- 
scope : whatever portion of the moon be visible, 
the edge is everywhere rough, with lines and 
points projecting beyond its general line, and with 
some insulated points completely beyond that line, 
and not connected with it by any lines of light. It 
is evident that the former must be elevated ridges 
rising above the general surface of the moon ; the 
latter, single points yet more elevated, and more 
distant from the part generally enlightened. We 
conclude, therefore, that the surface of the moon is 
everywhere rugged, without any great plains or 
large spaces, like the sea here, covered with 
water or any fluid, which, from the laws regulating 
the equilibrium of fluids, would necessarily have a 
smooth surface. 

It may seem that corresponding appearances 
ought to be presented by the other limb of the 
moon, and that, just as the sun's rays enlighten 
prominent objects beyond that part of her surface 
which he generally shines upon, we ought also to 
be able to see prominent points beyond the part 
of the moon directly turned towards us. And it is 
so; but, though such points are actually presented 



to our view, they are scarcely distinguishable to 
our senses, even when assisted by powerful instru- 
ments. It will be worth while to explain the cause 
of this difference, especially as it will show also 
how we are enabled to estimate the height of lunar 

B A 




mountains. For this purpose, let the arc C A 
represent a part of the moon's surface, and SAB 
any straight line touching it ; and let B be any 
point in that line, and join B with M, the centre of 
the moon. The part of the line B C, intercepted 
between B and the surface of the moon at C, is 
evidently the height of the point B above that sur- 
face; and whenever the angle A M C is small, 
B C is much less than A B. Now the rays of light 
move in straight lines ; S A B, therefore, may repre- 
sent the course of a ray of light. A, where it 
touches the sphere, will be a point in the general 
boundary of light and darkness ; but if B represent 
the top of a lunar mountain, Avhose height is C B, 
B will just receive the ray SAB, and will therefore 
be visible. The distance, A B, from the general 
boundary of light and shade, may be observed. It 
will not indeed be seen, except in particular cases, 
perpendicularly to the line joining the observer and 
the moon; but from the observed distance the 
real distance of A B may be computed, the inclina- 
tion at which it is seen being known ; and from the 
real distance, as computed, the angle A M B, and 
the height B C, may be ascertained. A B is neces- 
sarily greater than B C ; but this, though it is one, 
is not the only reason why the distance of an elevat- 
ed point from the boundary of the enlightened part 
of the moon is more easily observed than its actual 
prominence. We may now suppose S to represent 
the direction of an observer upon the earth; in 
which case it is plain that A will represent a point 
in the boundary of that part of the moon which, if 
she were perfectly smooth, would be visible from S. 
The observer at S, however, will be able to see the 



136 



WONDERS OF THE HEAVENS. 



/ 



point B, if that be, as before, a point elevated above 
the general surface of the moon ; but he will see it 
in the line S A B, or in the same direction with the 
point A, the extreme point of that part of the moon, 
which, independently of these prominences, would 
be presented to him : and he will not distinguish it 
as projecting beyond the general surface of the 
moon, though it is only by virtue of this projection 
that it is brought within his view at all. A similar 
mountain situated between the points A and C 
would indeed project beyond the line A B, and be 
partly distinguishable ; and in the extreme case of 
its being situated exactly at A, it would project 
thus by its whole height: but even then, as we 
have already seen, the prominence is much less 
than A B. ■ 

It will naturally be supposed that the nicety of 
observation required to detect such small quantities 
as the altitude of lunar mountains at the distance 
of the moon must be very great ; and their values 
may in consequence be considered as not very 
accurately ascertained. They were much overrated 
when first observed, and the observations then 
registered would correspond to surprising heights, 
as fifteen miles, or thereabouts. Better observa- 
tions, however, have reduced these extraordinary 
elevations; and Dr. Herschel considered few of 
these mountains to exceed half a mile in height. 
There are some, however, far higher; and one, in 
particular, named after the philosopher Leibnitz, 
has been computed by M. Schroeter to be twenty- 
five thousand feet, or nearly five miles, high. 

Besides these points near the illuminated edge of 
the moon, other bright points are occasionally seen 
in the dark parts of it, at so great a distance from 
the edge that they cannot be accounted for in the 
same manner : for a mountain lofty enough to be 
enlightened in such a position could not escape our 
observation when in the generally enlightened part 
of the moon. These points, therefore, when seen, 
must be luminous in themselves. They are seen 
occasionally, not always ; they are therefore lumi- 
nous only occasionally: and the most probable 
account that has been given of them is, that they 
are volcanoes, and that when they are visible, inde- 



pendently of reflected light, they are in a state of 
active eruption. Their appearance, when seen in 
the generally enlightened parts of the moon, corre- 
sponds with and confirms this supposition. 

If there be an atmosphere surrounding the moon, 
at all analogous to that of our earth, there must be 
twilight there ; and if there is twilight, there must 
be a partial and faint light beyond the boundary of 
that part of the moon which is fully and directly 
illuminated by the sun. Such a light has been 
actually observed, but very faint, and of small 
extent; corresponding therefore to the supposition 
of there being such an atmosphere, but of little 
power in reflecting light. That its power is very 
small, is evinced also by another consideration. 
The same media generally are powerful both in 
refracting and reflecting light. Now we have com- 
plete proof that the atmosphere of the moon has 
very little power in refracting light. In the course 
of the moon's revolution through the heavens, she 
must necessarily sometimes be in the same direction 
with some of the stars, and, being much nearer to 
us than they are, pass between us and them, and 
conceal them from us. This is called the occulta- 
tion of the fixed stars hy the moon. Her motions being 
known, the time at which that part of her which 
first coincides in position with a star does so 
coincide, or the beginning of the occultation, may 
be computed; and so, in the same manner, may its 
end, and consequently its duration.-. This, however, 
is the duration independently of any refraction by 
the moon's atmosphere : for it is deduced from con- 
sidering when the moon is exactly between the 
earth and the star, at which period it would inter- 
cept rays of light proceeding in a straight line from 
the star to the earth. If the moon have any 
refracting atmosphere, the duration would be 
shortened, for the rays would be bent towards the 
moon in passing through it, and, as they would 
pass first on one side of the moon, (that which first 
came in apparent contact with the star,) and after- 
wards on the other, (which last leaves it,) they 
would be bent towards each other, and towards the 
earth, and consequently in one case would continue 
to reach the earth after some part of the moon is 



;,7-jwwt»je--.;ii n „,*HMH«nyvT'*^»-''^n: "?,'■'■'•: '?*(»'*w»y 



IFgStagH HfaSBgM 



WONDERS OF THE HEAVENS 



137 



between the earth and star, and in the other would 
begin to arrive at the earth before the whole of the 
moon had passed from between them. The ob- 
served duration of the occultation would be less 
than the computed duration. Such a difference is 
in reality scarcely observable : its amount has never 
been A^ery completely ascertained, but it certainly 
does not exceed, in any case, eight seconds of time, — 
a diminution which is not greater than that which 
would correspond to a horizontal refraction not 
exceeding two seconds. The horizontal refraction 
at the earth is not less than thirty-three minutes ; 
and as, on the supposition of the medium being 
similar, the refracting power increases with the den- 
sity, it may be estimated from this, that the density 
of the lunar atmosphere must be nearly one thousand 
times less than that of ours. The identity of its 
nature, however, and, therefore, the conclusion 
drawn from it, is to a certain degree conjectural. 

One other circumstance respecting the lunar 
atmosphere may here be mentioned. It is clear 
that it is not loaded with heavy clouds, as the 
atmosphere of the earth so frequently is : for these 
would either themselves be visible to us, or would, 
at least, be discovered by the shadows they would 
cast upon the moon's surface. We can observe the 
shadows of her mountains, and should equally be 
able to observe those of her clouds. This observa- 
tion comes in aid of that already deduced from 
other appearances, of the absence of any large 
spaces covered with water, or any evaporable fluid 
in the moon; for, if there were any such, evapora- 
tion would take place, and clouds would be formed. 

Many of our conclusions with respect to objects 
on the surface of the moon are, to a certain extent, 
conjectural ; and it may possibly seem, that the 
conjectures are impugned by the dissimilarity of 
appearances presented by the moon and earth. 
Objects on the earth are seen by reflected light, as 
well as those at the moon ; yet with how much less 
brilliancy, except occasionally when a brightly- 
reflecting surface is met with, and with how many 
shades of color, instead of one uniform and almost 
white brightness, only diversified by its different 

degrees of intensity. And when we see objects 

18 



melted together in distance, and almost of uniform 
color, it is a pale bluish hue, of faint lustre. Any 
such objection may be removed by these considera- 
tions, — that the mixture of a great variety of colors 
will produce a white, or nearly a white, light, and, 
consequently, that the blended light reflected from 
a large distant tract ought, in general, to be nearly 
of that color ; that if the distant objects which we 
see on the earth are not so, it is because the rays 
which proceed from them pass through a long space 
of the lower and denser parts of our atmosphere, 
and the objects become, in consequence, tinged 
with its blue color; that their faintness proceeds 
partly from this cause, and partly from their being 
visible only in the strong light of day ; and that 
when the moon is seen so, also, there is not that 
striking difference in her appearance and theirs 
which we suppose, when we contrast them with 
our notion of her, as derived from common observa- 
tions in the darlmess of night. But it may be worth 
while to add, as a still further answer to any 
objections of this nature, the description which an 
accurate observer has given of the appearances 
presented by a part of the earth itself, where the 
brilliancy of the climate, and other accidental cir- 
cumstances, diminished some of the causes of differ- 
ence. 

" On the 26th of May we sailed from Valparaiso, 
and proceeded along the coast to Lima. During 
the greater part of this voyage, the land was in 
sight, and we had many opportunities of seeing not 
only the Andes, but other interesting features of 
the country. The sky was sometimes covered by 
a low, dark, unbroken cloud, overshadowing the 
sea, and resting on the top of the high cliffs which 
guard the coast ; so that the Andes, and, indeed, 
the whole country, except the immediate shore, 
were then screened from our view. But, at some 
places, this lofty range of cliffs was intersected by 
deep gullies, connected with extensive valleys, 
stretching far into the interior. At these openings 
we were admitted to a view of regions which, being 
beyond the limits of the cloud, and, therefore, 
exposed to the full blaze of the sun, formed a bril- 
liant contrast to the darkness and gloom in which 



138 



WONDERS OF THE HEAVENS 



we were involved. As we sailed past, and looked 
through, these mysterious breaks, it seemed as if 
the eye penetrated into another world; and had 
the darkness around us been more complete, the 
light beyond would have been equally resplendent 
with that of the full moon, to which every one was 
disposed to compare this most curious and surprising 
appearance." 

As the rays were not reflected from a bright, 
snowy surface, but from a dark-colored sand, we 
are furnished with an answer to the difficulties 
sometimes started respecting the probable dark 
nature of the soil composing the moon's surface. 



SECTION III. 

Kecurrence to the phenomenon called the new holding the old moon — 
Moon supposed by some to be phosphorescent — Leslie's explana- 
tion of the thread of light connecting the horns of the new moon — 
True explanation — Surface viewed through a telescope — Mountains 
and hollows — Lunar volcanoes — Arguments respecting the atmo- 
sphere — Is the moon inhabited ? — Discovery of a fortification and 
of roads in the moon. 

If we observe the moon in serene weather, when 
she is three or four days old, the part of her disc 
which is not enlightened by the sun is faintl}^ illu- 
minated by the light that is reflected from the 
earth, and the horns of the enlightened part appear 
to project beyond the old moon, as if they were 
part of a sphere considerably larger in diameter 
than the unenlightened part. This appearance has 
been expressively called, in common parlance, as 
was before stated, the new moon holding the old 
moon in her arms. It was once deemed a sufficient 
explanation of it to say, that bright objects affected 
the retina to a greater distance than those which 
were less luminous, and that, as ink sinks upon 
soft paper, the image of the bright part of the moon 
expands on the retina, and gives it the appearance 
of projecting beyond the darker portion of her disc. 
The explanation of this phenomenon is thus given 
by Dr. Jurin. He supposes that the eye cannot 
accommodate itself, with sufficient distinctness, to 
view objects at such a distance as the moon. The 



pencils of rays unite before they reach the retina, 
and form an indistinct and enlarged image of the 
moon. It may be proved by cutting out a piece of 
white paper, to represent the moon, and placing it 
upon a dark ground. When this luminous body is 
viewed either at a distance too remote or too near 
for perfect vision, its image on the retina will be 
enlarged, and the illuminated part will encroach 
upon the obscure portion, and appear to embrace 
it, in the same way as it is seen in the heavens. 
We must, however, take it for granted, that the 
eye cannot see the moon with perfect distinct- 
ness, — a position which does not rest upon the 
evidence of experiment. 

The less illuminated portion of the moon's disc, 
when she is three or four days old, obviously 
receives its light from the earth, which to the lunar 
inhabitants will then appear to be nearly full. As 
the age of the moon increases, this secondary light 
is gradually enfeebled, both in consequence of the 
diminution of the luminous part of the earth, and of 
the increase of the enlightened part of the moon. 
On one occasion, however, the weather being 
uncommonly favorable, Brewster states that he 
observed the secondary light when the moon was 
nearly ten days old. 

Riccioli and Leslie supposed the moon to be 
phosphorescent. They conceived it impossible to 
account in any other way for the extreme brilliancy 
of her disc. And Leslie explained, on this hypo- 
thesis, the thread of light which seems to connect 
the two horns of the moon. His theory is thus 
stated by himself: — " After emerging from con- 
junction with the sun, the moon's sharp horns are 
seen to be connected by a silver thread, which 
completes the circle ; and a very faint light seems 
to be suffused over the included space. This bright 
arch, however, becomes gradually less vivid, and 
before the moon is five or six days old, it has 
almost totally vanished. The pale outline of the 
old moon is commonly ascribed to the reflection 
from the earth; but if it were derived from that 
source, it would appear densest near the centre, 
and gradually dimmer toward the edge. I rather 
refer it to the spontaneous light which the moon 



=mra< 



WONDERS OF THE HEAVENS 



139 



may continue to emit for some time after the phos- 
phorescent substance has been excited by the action 
of the solar beams." 

" The lunar disc is visible when completely in the 
shadow of the earth ; nor can this fact be explained 
by the inflection of the sun's rays in passing through 
our atmosphere ; for why does the rim appear so 
brilliant ? Any such inflection could only produce 
a diffuse light, obscurely tinging the boundaries of 
the lunar orb ; and in this case the earth, presenting 
its dark side to the moon, would have no power to 
heighten the effect by reflection. But even when 
this reflection is greatest, about the time of con- 
junction, its influence seems extremely feeble. 
The lucid bounding arc is occasioned by the narrow 
lunula, which, having recently felt the solar im- 
pression, still continues to shine, and, from its 
extreme obliquity, glows with concentrated effect." 

The phenomenon thus described is represented 
in the accompanying plate, where a diluted light 




appears to be shed over the obscure portion of the 
moon's disc, while a lucid bow, more bright than 
the rest of the obscure part, seems to join the lunar 
horns. When we examine this luminous bow in 
the heavens, the lower part of it, at a, is always 
much broader than the upper part, at h; and when 



the moon has considerable libration, so as to with- 
draw from the earth a portion of the eastern limb, 
the bow ceases to be continuous, and the part at b 
is no longer visible. These two appearances, 
which Brewster states he has often observed, are 
sufficient to overthrow the explanation that has 
been already given ; for, upon that hypothesis, the 
lucid bow ought to have been broader in the centre, 
diminishing towards the horns, exactly like the 
enlightened part of the moon's disc. We are not, 
however, confined to arguments like this. The 
true explanation is so simple and convincing that it 
is scarcely possible not to adopt it. If we look at 
the maps of the moon here given, we shall find that 
the eastern limb is separated from the central parts 
of her disc by darker regions, and that the luminous 
portion between these darker regions and the 
circular line that bounds her eastern limb, has 
actually the form of a bow, broadest towards the 
southern horn, and gradually diminishing in breadth 
towards her northern horn. 

The immediate cause, therefore, of the lucid bow 
is to be sought for in the accidental circumstance 
of the moon's eastern limb being more luminous 
than the adjacent regions towards the centre. The 
central parts, indeed, are equally luminous with 
the eastern limb, but their brilliancy is impaired by 
their proximity to the illuminated portion. We 
see, then, the reason why the bow is broadest at a 
and narrowest at b, and why the libration of the 
moon, withdrawing the narrow part b of the bow, 
destroys its continuity. This may be better under- 
stood by comparing the preceding plate with the 
maps of the moon. 

When the surface of the moon is viewed with 
good telescopes, its appearance is found to be 
wonderfully diversified. Besides the large dark 
spots, which are visible to the naked eye, extensive 
valleys are distinguishable, and long ridges of ele- 
vated mountains, projecting their shadows on the 
plains below. Single mountains occasionally rise 
to a great height, while hollows, more than three 
miles deep, and almost exactly circular, exist in the 
plains. The margin of these cavities is often ele- 
vated a little above the general level, and a high 



140 



WONDERS OF THE HEAVENS 



eminence rises in the centre of the cavity. When 
the moon approaches to her opposition, the eleva- 
tions and depressions upon her surface in a great 
measure disappear, while her disc is marked w^ith 
a number of brilliant points and permanent radia- 
tions. 

It may be observed vi^ith a common telescope, 
that the lunar surface is not only diversified vt^ith 
rocks and cavities, but that some parts of it are 
distinguished from others by their superior illumi- 
nation. The dark parts of the disc are alw^ays 
smooth and apparently level, while the luminous 
portions are tracts which either rise into high . 
mountains or sink into deep and extensive cavities, 
The general smoothness of the obscure regions 
naturally induced astronomers to believe that they 
were large collections of water. If, however, we 
examine the disc with minute attention, we shall 
find that these obscure portions are not exactly 
level, like a fluid surface. In many of them the 
inequality of surface and of light is considerable, 
and in some parts parallel ridges are visible. The 
large dark spot on the moon's western limb, called 
the Crisian Sea, appears in general to be extremely 
level; but it has been observed, when the moon 
was a little past her opposition, and the boundary 
of light and darkness passed through the Crisian 
Sea, that this bounding line, instead of being ellipti- 
cal, as it would have been were the surface fluid, 
was irregular, and indicated that this portion of the 
disc was elevated in the middle. The light of 
these obscure regions varies much, according to 
the angle of illumination or the altitude of the sun 
above their horizon ; and when the moon is near 
her conjunction, they are not much less luminous 
than the other parts of the disc. This could not 
happen if they were covered with water. It is 
thought, then, that there is no water in the moon, 
such as rivers, lakes, or seas, and therefore none 
of those atmospherical phenomena which on our 
globe are owing to the existence of water. 

The strata of mountains, and the insulated hills, 
which mark the disc of this luminary, have no 
analogy with those of our globe. Her mountainous 
scenery bears a stronger resemblance to the tower- 



ing sublimity and the terrific ruggedness of Alpine 
regions, than to the tamer inequalities of less 
elevated countries. Huge masses of rocks rise at 
once from the plains, and stretch their peaked 
summits to an immense height in the air, while 
projecting crags spring from their rugged flanks, 
and, threatening the valleys below, seem to bid 
defiance to the laws of gravitation. Around the 
base of these frightful eminences are strewed 
numerous loose and unconnected fragments, which 
time seems to have detached from their parent 
mass ; and when one examines the rents and 
ravines which accompany the overhanging cliffs, 
he expects every moment that they are to be torn 
from their base, and that the process of destructive 
separation, that we had only contemplated in its 
effects, is about to be exhibited before us in tre- 
mendous reality. The strata of lunar mountains 
called the Appenines, that traverse a portion of 
her disc from north-east to south-west, rise with a 
precipitous and craggy front from the level of the 
" Stormy Sea." In some places their perpendicu- 
lar elevation is above four miles, though they often 
descend to a much lower level. To the north-east 
they present an inaccessible barrier, while on the 
south-west they sink in gentle declivity to the 
plains. 

On examining the circular cavities, it is found 
that the analogy between the surface of the moon 
and earth fails in a still more remarkable degree. 
Some of the immense caverns are nearly four miles 
deep, and forty in diameter. A high annular 
ridge, marked with lofty peaks and little cavities, 
generally encircles them. An insulated mountain 
frequently rises in their centre, and sometimes they 
contain smaller cavities of the same nature with 
themselves. These hollows are most numerous 
in the south-west part of the moon ; and it is from 
this cause that that portion is more brilliant than 
any other part of her disc. The ridges which 
encircle the cavities reflect the greatest quantity 
of light, and, from their lying in every possible 
direction, they appear, near the time of full moon, 
like a number of brilliant radiations. If these 
hollows be adorned with verdure, they must pre- 



WONDERS OF THE HEAVENS 



141 



sent to the view of a spectator, placed among them, 
a more variegated, romantic, and sublime scenery, 
than is to be found on the surface of our globe. 
An idea of some of these scenes may be acquired 
by conceiving a plain of about a hundred miles in 
circumference, encircled with a range of mountains, 
of various forms, three miles in perpendicular 
height, and having a mountain near the centre, 
whose top reaches a mile and a half above the 
level of the plain. From the top of this central 
mountain, the whole plain, with all its variety of 
objects, would be distinctly visible ; and the view 
would appear to be bounded on all sides by a lofty 
amphitheatre of mountains, in every diversity of 
shape, rearing their summits to the sky. From 
the summit of the circular ridge, the conical hill in 
the centre, the opposite circular range, the plain 
below, and some of the adjacent plains which 
encompass the exterior ridge of the mountains, 
would form another variety of view ; and a third 
variety would be obtained from the various aspects 
of the central mountain, and the surrounding 
scenery, as viewed from the plains below. 

Astronomers have found it difficult to explain, 
with any degree of probability, the formation of 
these immense cavities. Some have thought that 
our globe would present the same appearance if all 
the lakes and seas were removed. The lunar 
cavities, then, may be intended for the reception of 
water, or they may be the beds of lakes and seas 
that once existed in the moon. 

The deep caverns, and the broken, irregular 
ground, which appear in almost every part of the 
moon's surface, have induced several astronomers 
to believe that these inequalities are of volcanic 
origin. Their conjectures have received some con- 
firmation from a number of phenomena that have 
been seen in the dark part of the moon. 

During the annular eclipse of the sun, in 1778, 
Ulloa observed, before the edge of the sun's disc 
emerged from that of the moon, a bright white 
spot, which he imagined to be the light of the sun 
shining through an opening in the moon. This 
phenomenon continued about one minute and a 
quarter, and was noticed by difierent observers. 



Beccaria observed a similar spot in 1772, and sup- 
posed that it, as well as that perceived by Ulloa, 
was the flame of a burning mountain. Similar 
bright spots have been seen at various times. We 
shall not stop to enumerate them, but shall proceed 
to give, in his own words, Herschel's account of 
similar phenomena, which he witnessed in 1787. 

" April 19th. I perceive three volcanoes in dif- 
ferent places of the dark part of the new moon. 
Two of them are either nearly extinct or going to 
break out. This may perhaps be decided at the 
next lunation. The third shows an actual eruption 
of fire or luminous matter. Its light is much 
brighter than the nucleus of the comet that 
Mechain discovered on the 10th of this month. 

"April 20th. The volcano burns with greater 
violence than last night. I believe its diameter 
cannot be less than three seconds. Hence, the 
burning or shining matter must be above three 
miles in diameter. It is of an irregular, round 
figure, and very sharply defined on the edges. 
The other two volcanoes resemble large, faint 
nebulae, that are gradually brighter in the middle; 
but no well-defined luminous spot can be discerned 
in them. I did not perceive any similar phe- 
nomena last lunation, though I then viewed the 
same places with the same instrument. 

" The appearance of what I have called the actual 
fire exactly resembled a small piece of burning 
charcoal, when covered with a thin coat of white 
ashes; and it had a degree of brightness about as 
strong as such a coal would present in faint day- 
light. 

"All the adjacent parts of the volcanic mountain 
seemed to be faintly illuminated by the irruption, 
and were gradually more obscure as they lay at a 
greater distance from the crater." 

The formation of craters in different parts of the 
moon seems also to indicate the existence of volca- 
noes. With an excellent telescope, five feet long, 
and with an aperture of three inches and three 
quarters, Olbers discovered two small craters, 
which were wanting in Shroeter's charts. Shroeter 
had frequently examined this part of the moon, but 
had not perceived the slightest traces. He, how- 



142 



WONDERS OF THE HEAVENS 



ever, at last perceived the largest of them, which 
was uncommonly deep in proportion to its breadth, 
and was surrounded with abroad annular elevation, 
of little brightness. 

In order to convey an idea of the lunar surface, 
three plates are here given. Figure 1 is a very 




brilliant spot, called Aristarchus, in the north-east 
quarter of the moon's surface. Figure 2 represents 
the spot called Gassendi, in the south-east quarter, 
the dark edge a b representing the boundary be- 
tween the illuminated and obscure portion of her 
disc. Figure 3 is a spot called Hevelius, containing 
an annular cavity, and a broken elevation resem- 
bling an egg. 

As to the existence of a lunar atmosphere, there 



is much diversity of opinion among philosophers. 
The constant serenity of the moon's surface has 
induced some to believe that she had no atmo- 
sphere; and this opinion was confirmed by the 
brilliancy of light retained by the fixed stars and 
planets when they were nearly in contact with the 
limb of the moon, and when their light must have 
passed through her atmosphere if she had any. 
Fouchy endeavors to show, that the duration of 
eclipses and occultations ought to be diminished by 
means of the refractive power of the moon's atmo- 
sphere, and, if its horizontal refraction amounted to 
eight seconds, that there never could be a total 
eclipse of the sun. In that which happened in 
1724, total darkness continued two and one fourth 
minutes, — a circumstance which Fouchy maintains 
could not have happened had the moon been encir- 
cled with the rarest atmosphere. 

Yet, the appearance of the moon's limb in total 
and partial eclipses of the sun, has suggested 
numerous arguments for the existence of a lunar 
atmosphere. In 1605, Kepler perceived that the 
moon, in a solar eclipse, was surrounded with a 
luminous ring, most brilliant on the side nearest 
the moon. . A similar phenomenon was observed 
in the total eclipse of 1706. An observer of the 
same eclipse, at Bern, perceived a blood-red streak 
of light immediately before the emersion of the 
sun's limb. Fatio, at Geneva, observed the lumi- 
nous ring round the moon, and Scheuchyer describes 
the eclipse as appearing annular, in consequence 
of the refraction of the sun's light by the moon's 
atmosphere. In the total eclipse of 1715, Halley 
observed a diminution of brightness in the limb of 
the sun which was immerging before total darkness. 
The sharp horns of the solar crescent were blunted 
at their extremities during total darkness, and a 
ring of light encompassed the moon. The ring was 
brightest near the body of the moon, and flashes of 
light seemed to dart out on all sides from behind 
the moon a little before the emersion. About two 
seconds before the emersion, a long, narrow streak 
of dusky, but strong red light seemed to color the 
western limb of the moon; but when the sun 
appeared, the streak and the ring instantly vanished. 



WONDERS OF THE HEAVENS. 



143 



Louville saw the same phenomena, and describes 
the red streak as a piece of a circle, of a lively 
red, which preceded the emersion. 

In an eclipse of the sun, (1748,) when the un- 
covered part of that luminary resembled the moon 
in quadrature, the horns of the solar crescent were 
observed to be bent outward beyond the circle in 
which every other part of his disc was compre- 
hended. When the eclipse became annular, the 
sun's disc was dilated beyond the circle that 
formerly embraced it. This dilation Euler esti- 
mated at twenty-five seconds. 

In the eclipse of 1778, in which the solar dark- 
ness lasted four minutes, several singular appear- 
ances were observed. The ring of light about the 
moon seemed to have a rapid circular motion. 
This light became more dazzling as the centres of 
the bodies approached, and, about the middle of 
the eclipse, its breadth was a sixth part of the 
moon's diameter. Flashes issued from it in all 
directions : the light was reddish toward the moon, 
a deep yellow toward the middle, and a pure white 
at its circumference. 

Experiments were made with the shadows of 
globes by Maraldi and Fouchy, to show that the 
luminous ring might arise from another cause than 
the moon's atmosphere. They found that a ring of 
light, produced by the inflection of the passing rays, 
surrounded the shadows of all opaque globular 
bodies. But as the phenomena of inflection are 
produced merely by the surfaces of bodies, the 
breadth of the luminous ring produced by the head 
of a pin will be as great as that produced by the 
inflection of the moon at the same distance from 
both bodies. Thus the ring of light surrounding 
the moon would not exceed the ring seen by 
Maraldi around the globes of wood and stone, and 
therefore could not be discerned at the distance of 
that luminary. 

The appearance of the stars and planets, when 
eclipsed by the moon, also furnishes proofs of the 
existence of a lunar atmosphere. It was natural to 
expect, that when the stars or planets came in 
contact with the moon's limb they would suffer a 
change in color, arising from the transmission of 



their light through the densest part of the moon's 
atmosphere. When we consider, however, that 
this atmosphere, if its size were proportional to 
that of the earth, could not subtend a greater angle 
than one second, and that the emerging star moves 
through this space in two seconds of time, we can 
scarce expect any great change in its brilliancy. 
The visible limb of the moon may be formed by 
mountains, and the denser part of her atmosphere 
may be below their summits ; so that the remaining 
part of her atmosphere, which alone is visible to 
us, may not have suflScient density to deaden the 
light of the star. Cassini frequently observed the 
circular figure of Jupiter, Saturn, and the fixed 
stars, changed into an elliptical one, when they 
approached the limb of the moon. In an occulta- 
tion of Saturn, in 1762, the ring and body of that 
planet were observed to be affected by their 
proximity to the moon, and had the appearance of 
a comet at the moment of emersion. 

But the complete discovery of the moon's atmo- 
sphere was reserved for Schroeter. He had fre- 
quently perceived that the high ridges of certain 
lunar mountains, when in the dark hemisphere, were 
less illuminated in proportion to their distance from 
the boundary of light and darkness, and that the 
cusps were also more faintly illuminated than the 
other parts of the disc. He observed, also, changes 
in the lunar atmosphere, from which he was led to 
expect that a twilight might be perceived toward 
her cusps, as had been done in Venus. 

By observing the moon when her phases were 
extremely falcated, Schroeter at last discovered 
a faint, glimmering light, of a pyramidal form, 
extending from both cusps into the dark hemisphere. 
The greatest breadth of this light was two seconds, 
and its length one minute and twenty seconds; 
from which Schroeter computed that the breadth 
of the lunar twilight from the boundary of light 
and darkness to where it loses itself in, and assumes 
the faint appearance of, the light reflected from the 
earth, measures, in a direction perpendicular to the 
boundary of light and darkness, about two and a 
half degrees, and, therefore, that the inferior or 
more dense part of the atmosphere is not more than 



144 



WONDERS OF THE HEAVENS 



fifteen hundred feet high, and that the height where 
it could affect the brightness of a fixed star, or in- 
flect the solar ray, is not so much as six thousand 
feet. This space subtends at the earth an angle 
of less than a second, and which would be passed 
over by a star in less than two seconds of time. 
A spectator on the lunar surface would behold the 
earth, like a luminous orb suspended in the dome 
of heaven, presenting a surface about thirteen times 
larger than the moon does to us, and appearing 
sometimes gibbous, sometimes horned, and at other 
times with a round, full face. The light which the 
earth reflects upon the dark side of the moon may 
be perceived by a common telescope. The lunar 
surface contains about fifteen millions of square 
miles, and is, therefore, capable of containing a 
population equal to that of our globe, allowing 
fifty-three inhabitants to every square mile. That 
this planet is inhabited by sensitive and intelli- 
gent beings, there is every reason to conclude, 
from a consideration of the sublime scenery with 
which its surface is adorned, and of the general 
beneficence of the Creator, who appears to have 
left no large portion of his material creation with- 
out animated existences ; and it is highly probable 
that direct proofs of the moon's being inhabited may 
hereafter be obtained. Indeed, if we are ever to 
obtain an ocular demonstration of the habitability of 
any of the celestial orbs, the moon is the only one 
where we can expect to trace, by our telescopes, 
indications of the agency of sentient or intelligent 
beings ; and we are convinced, that a long-continued 
series of observations on this planet, by a number 
of individuals, in different places, might completely 
set at rest the question whether the moon be a 
habitable world. Were a vast number of persons, 
in different parts of the world, to devote themselves 
to a particular survey of the moon — were different 
portions of her surface allotted to different indi- 
viduals, as the object of their particular research — 
were every mountain, hill, cavern, cliff", and plain, 
accurately inspected, and every change and modi- 
fication in the appearance of particular spots care- 
fully marked and represented in a series of delinea- 
tions — it might lead to some certain conclusions, 



both as to her physical constitution and her ultimate 
destination. It can be demonstrated, that a tele- 
scope which magnifies one hundred times will show 
a spot on the moon's surface whose diameter is 
twelve hundred and twenty-three yards ; and one 
which magnifies a thousand times will, of course, 
enable us to perceive a portion of her surface whose 
size is only one hundred and twenty-two yards: 
and, consequently, an object, whether natural or 
artificial, of no greater extent than one of our large 
edifices, (for example, St. Paul's Church, London,) 
may, by such an instrument, be easily distinguished. 
Now, if every minute point on the lunar surface 
were accurately marked by numerous observers, it 
might be ascertained whether any changes are 
taking place, either from physical causes, or from 
the operations of intelligent agents. If a large 
forest were cutting down — if a city were building 
in an open plain, or extending its former bounda- 
ries — if a barren waste were changing into a scene 
of vegetation — or, if an immense concourse of 
animated beings were occasionally assembled on a 
particular spot, or shifting from one place to 
another — such changes would be indicated by 
certain modifications of shade, color, or motion; 
and, consequently, would furnish a direct proof of 
the agency of intelligent beings analogous to man, 
and of the moon being a habitable globe. For, 
although we may never be able to distinguish the 
inhabitants of the moon, (if any exist,) yet, if we can 
trace those effects which can flow only from the 
operations of intelligent agents, it would form a 
complete demonstration of their existence — on the 
same ground on which a navigator concludes an 
unknown island to be inhabited, when he perceives 
human habitations and cultivated fields. 

" That changes occasionally happen on the lunar 
hemisphere next the earth, appears from the 
observations of Herschel and Schroeter, particu- 
larly from those of the latter. In the Transactions 
of the ' Society of Natural Philosophy,' at Berlin, 
Schroeter relates that on the 30th December, 1791, 
at 5 o'clock, P. M., with a seven-feet reflector, 
magnifying one hundred and sixty-one times, he 
perceived the commencement of a small crater on 



■.ifies^a 



¥>tBS'C©FK "flaw ©1' iPgg M#® 



"flKIl ®t© iM®®W = 




<^^ 



^r? 






WONDERS OF THE HEAVENS 



145 



the south-west declivity of the volcanic mountain 
in the Mare Crisium, having a shadow of at least 
2". 5. On the 11th January, at twenty minutes 
past five, on looking at this place again, he could 
see neither the new crater nor its shadow. Again, 
on the 4th January, 1792, he perceived, in the 
eastern crater of Helicon, a central mountain, of a 
clear gray color, three seconds in diameter, of 
which, during many years' observations, he had 
perceived no trace. ' This appearance,' he adds, 
' is remarkable, as, probably, from the time of 
Hevelius, the western part of Helicon has been 
forming into its present shape, and nature seems, 
in that district, to be particularly active.' In 
making such minute observations as those to which 
we have alluded, it would be proper, along with an 
inspection of the moon's luminous disc, to mark the 
appearances of different portions of her dark hemi- 
sphere, when it is partially enlightened by the 
reflected light from the earth, soon after the 
appearance of new moon. These researches would 
require a long- continued series of the most minute 
observations, by numerous observers in different 
regions of the globe, which could be effected only 
by exciting, among the bulk of mankind, a general 
attention to such investigations. But were this 
object accomplished, and were numerous observa- 
tions made from the tops of mountains, and in 
the serene sky of southern climes, where the 
powers of the telescope are not counteracted by 
dense vapors, there can be little doubt that direct 
proofs would be obtained that the moon is a habita- 
ble world ; or, at least, that the question in relation 
to this point would be completely set at rest." 

The public was once amused by the announce- 
ment of a discovery said to have been made by 
Professor Frauenhofer, of Munich. This gentleman 
was said to have discovered a fortification in the 
moon, and to have distinguished several lines of 
road, supposed to be the work of the lunar inhabi- 
tants. It is scarcely necessary to say, that such 
announcements are obviously premature. To per- 
ceive distinctly the shape of an object in the moon, 
which resembles a fortification, it is requisite that 

that object be of a much larger size than our 
19 



terrestrial ramparts. Besides, although an object 
resembling one of our fortifications were perceived 
on the surface of the moon, there would be no 
reason to conclude that it served the same purpose 
as fortifications do among us. We are so much 
accustomed to war in our terrestrial system, and 
reflect so little on its diabolical nature, that we are 
apt to imagine that it must form a necessary 
employment even in other worlds. With regard 
to the pretended discovery of the lunar roads, it 
may not be improper to remark, that such roads 
must be at least four hundred feet broad, or ten 
times the breadth of ours, in order to be perceived 
as faint lines through a telescope which magnifies a 
thousand times ; which is a higher power, we pre- 
sume, than Frauenhofer can apply with distinctness 
to any of his telescopes.* It is not at all likely that 
the lunar inhabitants are of such a gigantic size, or 
employ carriages of such an enormous bulk, as to 
require roads of such dimensions, since the whole 
surface of the moon is only the thirteenth part of 
the area of our globe. 

Schroeter conjectured the existence of a great 
city to the north of Marius, (a spot in the moon,) 
and of an extensive canal towards Hygens, (another 
spot,) and he represented part of the spot named 
Mare Imbrium to be as fertile as the Campania. 
Similar remarks to those now stated will apply to 
these conjectures of Schroeter. We are too apt to 
imagine that the objects we perceive in the moon 
must bear a certain resemblance to those with 
which we are acquainted on the earth ; whereas, 
there is every reason to believe, from the variety 
we perceive in nature, that no one world resembles 
another, except in some of its more prominent and 
general arrangements. The moon bears a general 
resemblance to the earth, in its being diversified 
with mountains and valleys ; but the positions and 
arrangement of these objects in the moon, and 
th-e scenery they exhibit, are materially different 
from what appears on the surface of our globe. 

* More recently, Professor Gruitliausen, of Munich, has publicly- 
declared that he has discovered irrefragable proofs that the moon is 
inhabited like the earth. All Europe has answered by railleries the 
declaration of the Bavarian astronomer, but his firmness has been 



CHAPTER V. 



SECTION I. 

The system of the world — Limits of magnitude and minuteness — 
Theories respecting the world — Ptolemy's — Egyptian — Tycho 
Brahe's — Copernican — Des Cartes' whirlpools — Number and names 
of the planets — Origin of their symbols — Their comparative dis- 
tances from the sun — Their division into inferior and superior — 
Their periodical times — Their secondaries — Origin of the planets' 
names — Heliocentric circle of a planet — Aspects, what — Venus 
both an evening and a morning star — Its phases — "Why imper- 
ceptible to the naked eye — Inferior planets — Their geocentric 
motions in looped curves — Mars — The form of its disc — Its orbit 
without the earth's — Aspects and motions of superior planets — 
Mode of determining the position of the orbits — Elements of an 
orbit — Predicting a planet's return to the same situation — Venus 
sometimes visible at noonday. 

To study nature is to search into the works of 
creation, where every step must lead us to form 
more exalted ideas of the divine Being who prevails 
throughout, directs and animates the whole. From 
the animalcule that is invisible to the unassisted 
eye, to the magnificent luminaries of heaven, he is 
everywhere present. 

What sublime ideas of this great Being do we 
obtain by contemplating the vast diversity of his 
works ! How is the mind captivated by the aston- 
ishing scenes that are spread out before us ! That 
part of nature which is the immediate object of our 
senses is very imperfect, and but of small extent ; 
yet, by the assistance of art and the help of reason, 
it is enlarged till it loses itself in an infinity on 
either hand. The immensity of things on one side, 

no more shaken than that of Christopher Columbus was when he 
announced the existence of a new world. The German journals 
have published the observations of Professor Gruithausen, combined 
with those of his learned brother, the astronomer Schroeter. Their 
common conclusions are, 1. That vegetation upon the surface of the 
moon extends to the fifty-fifth degree of latitude south, and to the 
sixty-fifth degree of latitude north ; 2. That from the fiftieth degree 
of latitude north to the forty-seventh degree of latitude south may be 
perceived evident traces of the abode of animated beings ; 3. That 
some signs of the existence of lunar inhabitants are sufl[iciently appa- 
rent to enable a person to distinguish great roads traced in several 
directions, and particularly a colossal building, situate nearly under 
the equator of the planet. The ensemble presents the aspect of a 
large town, near to which may be distinguished a building, perfectly 
resembling that which we call a redoubt. 



and their minuteness on the other, carry them 
equally out of our reach, and conceal from us many 
of the more admirable parts of physical operations. 
As magnitude, abstractly considered, is capable of 
being increased indefinitely, and is also divisible 
without end, so we find that in nature the limits 
of dimension are at an immense distance from each 
other. We can perceive no bounds to the vast 
expanse in which natural causes operate ; and we 
are no less at a loss when we endeavor to trace 
things to their elements, and to discover the limits 
which include the subdivisions of matter. 

The objects that we call great vanish when 
we contemplate the vast body of the earth ; and 
the earth, in its turn, is lost in the solar system. 
In some parts, it is seen only as a distant star; in 
others, it is unseen, or seen only at certain times, 
by vigilant observers, assisted, perhaps, by instru- 
ments like our telescopes. The sun itself dwindles 
into a star — Saturn's vast orbit, and the orbits of 
the comets, crowd into points — when viewed from 
numberless places between the earth and the 
nearest fixed stars. Other suns give light to illumi- 
nate other systems, where the rays of our sun are 
unperceived ; but these also are swallowed up in 
the immeasurable expanse. Even all the systems 
of the stars which sparkle in the clearest sky, must 
possess but a small part of that space over which 
such systems are dispersed, since more stars are 
discovered in one constellation, by the telescope, 
than the naked eye perceives in the whole heaven. 

And after we have proceeded thus far, and left 
all definite measures behind us, we find ourselves 
still no nearer to a limit ; for all this is nothing to 
what may be displayed in the infinite expanse 
beyond the remotest stars that have ever been 
discovered. 

We shall now proceed to give an account of 
some of the diiferent theories that have prevailed, 
at different times, concerning the solar system. 
They are various and contradictory. 



WONDERS OF THE HEAVENS 



147 



The most celebrated of those who established a 
hypothesis among the ancients, and who defended it 
with a show of reason and argument, was Ptolemy, 
called " the wisest and most divine among the Greek 
philosophers." He flourished at Alexandria, in 
Egypt, in the time of the emperor Adrian, about 
one hundred and thirty years after Christ. He 
supposed that the earth was fixed immovably in 
the centre of the universe, and that the moon. 
Mercury, Venus, the sun. Mars, Jupiter, and 
Saturn, revolved around it, according to the order 
mentioned. Above these, he placed the firmament 
of the fixed stars, the primum mobile, and coelum 
empyrium, or heaven of heavens ; all of which 
were imagined to move round the earth once in 
twenty-four hours, as also in certain other stated 
or periodical times, agreeably to their annual 
changes and appearances. And to account for 
their different motions, Ptolemy was obliged to 
imagine a number of curves, called eccentrics and 
epicycles, which crossed and intersected each 
other in various directions. 

This theory may be explained by reference to 
the figure below. Let ABC be a circle, S the 




centre, E the earth; abed another circle, whose 
centre, v, is in the circumference of the circle 
ABC. Conceive the circumference of the circle 
A B C to be carried round the earth every twenty- 
four hours, according to the order of the letters, 
and at the same time let the centre v of the circle 
abed have a slow motion in the opposite direction, 
and let a body revolve in this circle in the direction 
abed; then it is manifest, that, by the motion of 



the body in this circle, and the motion of the circle 
itself, the body might describe such a curve as is 
represented by klmbnop; and if we draw the 
tangents E /, Era, the body would appear sta- 
tionary at the points I and m, and its motion would 
be retrograde through Im, and then direet again. 
Now, to make Venus and Mercury always accom- 
pany the sun, the centre v of the circle abed was 
supposed to be always very nearly in a right line 
between the earth and the sun, but more nearly so 
for Venus than for Mercury, in order to give each 
its proper elongation. This system, although it 
will account for all the motions of the bodies, yet 
it will not solve the phases of Venus and Mercury ; 
for, in this case, in both conjunctions with the sun, 
they ought to appear dark bodies, and to lose their 
lights both ways from their greatest elongations ; 
whereas, it appears, from observation, that, in one 
of their conjunctions, they shine with full faces. 

This rude system was soon found incapable of 
standing the test of observation and experiment, 
and, notwithstanding the opposition of blind and 
zealous bigots, it has long been rejected by all 
mathematicians and philosophers. The planets 
Mercury and Venus are now well known not to 
include the earth in their orbits, and the comets 
move through the heavens in all directions, so that 
they must infallibly have met with continual ob- 
structions, and would long since have broken to 
pieces all the imagined crystal spheres, and ren- 
dered them totally unfit for the purposes for which 
they were designed. 

The contradictions and perplexities attending 
the theory of Ptolemy were, indeed, so numerous 
and evident, that it was impossible they shQuld 
ever be reconciled upon that hypothesis. Notwith- 
standing this, mankind were not easily induced to 
give up their darling prejudices, and embrace the 
truth in whatever form she might be presented. 
Many early habits were to be corrected, and vulgar 
prepossessions eradicated from the mind, before men 
could be brought to reckon the earth as a planet, 
and to believe this vast globe, which appears to 
be the most fixed of all things in nature, to be 
whirling round the heavens with such rapidity. 



148 



WONDERS OF THE HEAVENS. 



The system received by the Egyptians was this : 
that the earth is immovable in the centre, about 
which revolve, in order, the moon, sun, Mars, 
Jupiter, and Saturn — and about the sun revolve 
Mercury and Venus. This disposition will account 
for the phases of Mercury and Venus, but not for 
the apparent motions of Mars, Jupiter, and Saturn. 

The next system which we shall mention, though 
posterior in time to the true, or Copernican System, 
as it is usually called, is that of Tycho Brahe, a 
Polish nobleman. He was pleased with the Coper- 
nican system, as solving all the appearances in the 
most simple manner ; but conceiving, from taking 
the literal meaning of some passages in Scripture, 
that it was necessary to suppose the earth to be 
absolutely at rest, he altered the system, but kept as 
near to it as possible. And he further objected to 
the earth's motion, because it did not, as he con- 
ceived, affect the motions of comets observed in 
opposition, as it ought ; whereas, if he had made 
observations on some of them, he would have found 
that their motions could not otherwise have been 
accounted for. In his system, the earth is sup- 
posed to be immovable in the centre of the orbits 
of the sun and moon, without any rotation about an 
axis ; but he made the sun the centre of the orbits 
of the other planets, which, therefore, revolved 
with the sun about the earth. By this system, the 
different motions and phases of the planets may be 
solved, the latter of which could not be by the 
Ptolemaic system ; and he was not obliged to 
retain the epicycloids, in order to account for their 
retrograde motions and stationary appearances. 
One obvious objection to this system is, the want of 
that simplicity by which all the apparent motions 
may be solved, and the necessity that all the hea- 
venly bodies should revolve about the earth every 
day , whereas it is physically impossible that a large 
body, as the sun, should revolve in a circle about 
a small body, as the earth, at rest in its centre. 
If one body be much larger than another, the 
centre about which they revolve must be very near 
the large body, — an argument which holds also 
against the Ptolemaic system. It appears, also, 
from observation, that the plane in which the sun 



must, upon this supposition, diurnally move, passes 
through the earth only twice in a year. It cannot, 
therefore, be any force in the earth which can 
retain the sun in its orbit ; for it would move in a 
spiral, continually changing its plane. In short, 
the complex manner in which all the motions are 
accounted for, and the physical impossibility of 
such motions being performed, is a sufficient reason 
for rejecting this system ; especially when we con- 
sider in how simple a manner all these motions 
may be accounted for, and demonstrated, from the 
common principles of motion. Some of Tycho's 
followers, seeing the absurdity of supposing all the 
heavenly bodies daily to revolve about the earth, 
allowed a rotary motion to the earth, in order to 
account for their diurnal motion, and this was 
called the semi-Tychonic system; but the objections 
to this system are, in other respects, the same. 

Thus, instead of consulting the heavens, and 
collecting the history of nature, philosophers were 
ambitious to gratify their vanity, or their precon- 
ceived notions, by inventing whimsical hypotheses, 
which had no conformity to fact. Cycles and 
epicycles were multiplied, to answer every appear- 
ance, till the universe had lost all its native beauty 
in their descriptions, and seemed again reduced to 
chaos by their unhappy labors. 

The system which is now universally received is 
called the Copernican. Here the sun is placed in 
the centre of the system, about which the other 
bodies revolve, in the following order : Mercury, 
Venus, the Earth, Mars, Jupiter, Saturn, and Her- 
schel, which was discovered by Dr. Herschel ; 
beyond these, at immense distances, are placed the 
fixed stars. The moon revolves about the earth, and 
the earth revolves about an axis. This disposition 
of the planets solves all the phenomena, and in the 
most simple manner; for, from inferior to superior 
conjunction, Venus and Mercury appear first horned, 
then dichotomised, (halved,) and next gibbous, and 
the contrary from superior to inferior conjunc- 
tion. They are always retrograde in their inferior, 
and direct in their superior, conjunction. Mars 
and Jupiter appear gibbous about their quadratures ; 
but in Saturn and Herschel this is not sensible, on 



WONDERS OF THE HEAVENS 



149 



account of their great distances. The motions of 
the superior planets are observed to be direct in 
their conjunction, and retrograde in their opposi- 
tion. A]l these circumstances are such as ought 
to take place in the Copernican system. The 
motions, also, of the planets are such as should 
take place upon physical principles. We may also 
further observe, that the supposition of the earth's 
motion is necessary, in order to account for a 
small apparent motion which every fixed star is 
found to have, and which cannot otherwise be 
accounted for. The harmony of the whole is as 
satisfactory a proof of the truth of this system as 
the most direct demonstration could be : we shall 
therefore assume this system to be true. 

Among the modern philosophers, one, who 
attempted to explain the phenomena of nature by 
principles less exceptionable than those of the 
ancients, and who acquired a great reputation 
among his followers, claims, at least, a passing 
notice for his theory respecting the solar system. 

Des Cartes was the author of a new system, 
which, for a long time, divided the opinions of the 
learned, and was considered by many as the most 
extensive and exquisite in its contrivance of any 
that had been before imagined. Endowed with a 
bold and elevated genius, he attempted to unveil 
at once all the mysteries of nature, and thought it 
beneath him to offer any thing to the world less 
than a complete and finished system. 

To account for the motions of the celestial bodies, 
he supposes the sun to be placed in the centre of 
a vast whirlpool of subtle matter, which extends to 
the utmost limits of the system ; and the planets, 
being plunged into such parts of this vortex as are 
equal in density to themselves, are continually 
dragged along with it, and carried round their 
several orbits, by its constant circulation. Those 
planets that have satellites are likewise the centres 
of other smaller whirlpools, which swim in the great 
one; and the bodies that are placed in them are 
driven round their primaries in the same manner 
as those primaries are driven round the sun. 

Hence, as the sun turns upon its axis the same 
way as the planets move, and the primaries turn 



round their axes the same way as their satellites 
move round them, it was imagined, that, if the 
whole planetary region were filled with a fluid 
matter like that before mentioned, the sun and 
planets, by a constant and rapid rotation on their 
axes, would communicate a circular motion to 
every part of this medium, and by that means drag 
along the bodies that swim in it, and give them the 
same circumvolution. This is the celebrated system 
of vortices, and the world, of Des Cartes. However 
absurd or romantic this may seem now, when first 
stated it divided the whole philosophic world into 
two great parties. 

The solar system consists of the sun, with the 
planets and comets, which perform their revolutions 
around him. In the midst apparently of a vast 
concavity, surrounded every way with stars, which 
are at an immense distance from the sun and from 
each other, is the great central luminary, whilst 
eleven planets and several comets perform their 
revolutions around him, at different distances from 
him, and in different periods of time. 

The planets may be considered as so many 
earths, enlightened and warmed by the sun in 
different degrees, inhabited by creatures rational 
and irrational, and, it may be, very different from 
those on our globe. To inhabitants of these planets 
the earth, if visible, would appear like the rest of 
the primaries. The names of the planets, in the 
order of their distance from the sun, with their 
respective symbolical characters, are as follows:— 
^ Mercury ; ? Venus ; 9 Earth ; $ Mars ; g Ves- 




ta; t? Juno; ? Ceres; / Pallas; ^ Jupiter; 
h Saturn; ^ Herschel. An origin has been 



n.imu'wij jn niyMJMMtiHaM 



oafiBORKBiea! 



150 



WONDERS OF THE HEAVENS 



ascribed to these characters which will be under- 
stood by a reference to the accompanying plate. 
They were taken from the symbols of those heathen 
deities whose names they bear. Thus, the character 
of Mercury, ^, is his caduceus, or rod, with ser- 
pents twined about it; that of Venus, 9 , a looking- 
glass, with a handle, such being the form of the 
ancient mirrors ; that of Mars, $ , a buckler and 
spear; that of Saturn, h, a sickle; that of Jupi- 
ter, 21, is Z, the first letter of his name in Greek, 
(Zeus,) with a stroke through it to denote abbre- 
viation. To this we may add that the sun's char- 
acter, O, represents a buckler, as the ancients 
kept their bucklers bright to dazzle the eyes of 
their enemies ; d , the moon, plainly represents a 
crescent ; 0, the earth, seems to represent a sphere, 
with the equator. As to the other planets, their 
discovery is of modern date. 

The comparative distances of the planets from 
the sun are as follows, the earth's being considered 
as unity: that of Mercury is t\; of Venus, tV; of 
Mars, Vs; of Vesta, 2-^xs; of Juno, 2j-V; of Ceres, 
2-1^; of Pallas, 2-1-^^; of Jupiter, b^^; of Saturn, 9h; 
ofHerschel, I'^tu. The following may be a more 
simple method of remembering the distances of the 
different planets from the sun. 

Write in a line the following series of numbers, 
the law of which is evident : — 

0, 3, 6, 12, 24, 48, 96, 192. 

Add four to the first six, and we have 

4, 7, 10, 16, 28, 52, 96, 192. 

It will be seen, by the signs placed under these 
numbers, that if 10 represents the distance of the 
earth from the sun, 4 will be the distance of Mer- 
cury; 7 that of Venus; 16, 52, 96, and 192, the 
respective distances of Mars, Jupiter, Saturn, and 
Uranus. 

The absolute distances will be given hereafter, 
and the method of finding those distances. When 
we compare the distances of the several planets 
from the sun in a looser and more general Avay, we 
call those inferior which are nearer the sun than 



the earth is, those superior which are further from 
the sun than the earth is. 

The periodical times in which the planets go 
round the sun, are as follows, in days and decimals 
Mercury, 87.97; Venus, 224.7; Earth, 365.3 
Mars, 686.98; Vesta, 1325.74; Juno, 1592.66 
Ceres, 1681.39; Pallas, 1686.54; Jupiter, 4332.6 
Saturn, 10759.2; Herschel, 30686.8, of our time. 

These are called primary planets. The four 
between Mars and Jupiter, being very small, have 
been named " asteroids," which signifies " similar 
to stars." Some of the planets are attended in 
their courses round the sun by certain smaller 
spherical bodies, which have been accordingly 
named secondaries, satellites, or attendants. Thus, 
our earth has one moon, Jupiter four, Saturn seven, 
and Herschel six. None of these, except our 
satellite, are visible without the aid of the tele- 
scope. 

The name Saturn (synonymous with time) seems 
to have been given to that planet from the apparent 
slowness of its motion; Jupiter, from its brightness; 
Mars^ (from the god of war,) because of its red fiery 
appearance ; earth, from its supposed want of 
splendor; Venus, from its beauty; Mercury, proba- 
bly, from the rapidity of its motion. 

The dominion of the heavenly bodies was fancied 
by the superstitious among the ancients, and, we 
grieve to add, by some Avho ought to know better 
among the moderns, to be so extensive, that the 
sun, moon, and planets, had each of them a particu- 
lar constellation or portion of the heavens assigned 
it, wherein being posited, they were supposed to be 
most powerful in their influence, and were therefore 
said to be in their exaltation; and when in the 
opposite part of the heaven they were said to be in 
their fall or detriment, and thought to be weak. 
Besides this, every one had its peculiar color, 
metal, stone, tree, flower, animal, number, day, 
&.C., assigned it, whence are derived the supposed 
virtues of amulets and talismans, for the dealers in 
these fooleries pretend that there is a sympathy 
between the heavenly bodies and those things 
which are under their dominion, so that, for in- 
stance, the plant over which any planet presided 



152 



WONDERS OF THE HEAVENS. 



had a power of attracting the influences of that 
planet. 

The paths or orbits of the planets round the sun 
may well enough be considered as concentric 
circles, having the sun in their common centre. In 
this view, they are represented in the accompanying 
plate, where, the sun being the centre, the smallest 
circle represents the orbit of Mercury, the next 
that of Venus : the orbits of the earth, Mars, 
the four small planets, Jupiter, Saturn, follow in 
their order, and are easily distinguished, as well by 
their several dimensions, as by being marked with 
the characters of their respective planets. Each of 
the elliptical curves represents a portion of the 
orbit of a comet. The remainders of the ellipses are 
to be conceived as extending far beyond the paper. 

The orbits of the planets are not in the same 
plane, as they are represented in the plate ; though 
the difference of the inclinations of their orbits is 
small, excepting those of Pallas, Juno, and Ceres. 
The mode of expressing the situation of the orbits, 
in this respect, is to take the plane of the earth's 
orbit as a standard, and compute the inclination of 
the several orbits to this. 

The heliocentric circle of a planet is that which 
the planet would appear to describe to a spectator 
in the sun. All very distant objects appear to us 
situated in some part of the sphere that we call the 
heavens. If, then, a spectator at the sun were to 
observe any planet, it would appear to him situated 
among the fixed stars ; and if he continued to observe 
it during its entire revolution, though it were in 
reality at a distance incomparably less than that of 
the stars, it would seem to him to describe a great 
circle on the starry sphere. This would be the 
heliocentric circle of the planet, because it is 
described by a line (the radius vector) drawn from 
the eye of an observer at the sun to the planet, and 
is always in the plane of that planet's orbit. 

We may say, generally, that to a spectator in 
the sun the several planets would appear to describe 
different circles in different periods of time. If 
these circles were all in the same plane, they 
would appear to coincide, that is, one circle would 
represent them all ; but as the planes of the planets' 



orbits are all different, the circles to represent them 
must be different; and since the times of their 
revolutions in their apparent circles are the same 
as their respective periods in their real orbits, there 
must be the same difference between the former as 
between the latter. 

The configurations of the heavenly bodies, aris- 
ing from their situations with regard to their differ- 
ent longitudes measured on the ecliptic, are called 
aspects ; as if they looked at one another in differ- 
ent manners, according to their positions. The 
term seems to have been adopted from a suppo- 
sition once entertained that the sun, moon, and 
planets, were animated beings. The framers of 
judicial astrology would have us believe that some 
of the heavenly bodies are of a benign, others of 
a malignant, nature, having more or less effect 
according to their aspects. Kepler, therefore, de- 
fined an aspect to "be an angle formed by the 
rays of the planets meeting on the earth, and hav- 
ing power to influence sublunary beings." 

We have already treated of the motions of the 
sun and moon. These two are more interesting to 
us than all the other heavenly bodies : the first 
because it is the principal source of life and fruit- 
fulness to the earth; the second because of its 
proximity, its beauty, its phases ; and both, because 
they furnish us the means of measuring time. Yet 
the other bodies which compose our planetary sys- 
tem reward our researches with results that are 
equally curious and useful. By studying them we 
shall attain a more perfect knowledge of the system 
of the universe, and this knowledge, in turn, will 
have an effect upon our first results, either correct- 
ing them by more exact measurements, or enabling 
us to regard them in a more extended connection, 
or, finally, discovering to us relations that had 
before escaped our observation; for the com- 
parison of many similar phenomena necessarily 
developes their analogies, and we learn to see the 
more, the more we practice observation. 

Encouraged by this belief, we enter with zeal 
upon the study of the planetary motions. We shall 
seek to discover their laws from a comparison of 
the phenomena they present. 



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WONDERS OF THE HEAVENS 



153 



Let us begin with Venus, which is the most con- 
spicuous. There is no one who has not remarked 
at times a beautiful star shining in the west a little 
after sunset, and called, for this reason, the evening 
star. This is the planet Venus. On observing it 
for several successive days, we perceive that it does 
not remain constantly at the same distance from the 
sun. It removes until it reaches a certain limit, 
which is about forty-five degrees, after which it 
seems to approach the sun again; and as we can 
commonly see it with the naked eye only when the 
sun is below the horizon, it is visible for a short 
time immediately after sunset. After some time 
has elapsed, it sets with the sun, and then, the 
splendor of the sun's light preventing us from per- 
ceiving it, we lose it entirely from our view. 

After some days, we discover in the morning, 
near the east, a beautiful star, which we had not 
observed there before. At first it rises but a few 
moments before the sun, and we name it, from this 
circumstance, the morning star. From day to day 
it removes further from the sun, and rises earlier 
and earlier ; but after having attained a distance of 
about forty-five degrees from that luminary, again 
approaches it, rises with it, and consequently ceases 
to be visible. 

Soon after, the evening star is again seen in the 
west, at a little distance from the sun. As this 
distance increases, it escapes from the splendor of 
the sun's rays. Afterward it approaches again, 
and again recedes, always following the same 
laws, and being in turn a morning or an evening 
star. 

These alternate motions, observed during more 
than two thousand years without interruption, 
plainly show that the morning and evening star 
are one and the same body. They also teach us 
that this star has a proper motion, and that, by 
reason of this proper motion, it seems to oscillate 
about the sun, appearing now as if preceding, and 
now as if following, that luminary. 

These are the appearances presented to the 
unaided eye ; but that excellent invention, the tele- 
scope, permits us to extend these observations much 

further. By this instrument that is revealed to us 
20 



which before was only imagined, viz., that Venus 
has phases, like the moon. 

In the evening, when it is approaching the sun, 
it appears as a luminous crescent, the horns of which 
are toward the east, that is, in a direction opposite 
the sun. The apparent size of this crescent dimin- 
ishes day by day, as the planet approaches the sun. 
But after it has passed the sun, and reappears, in 
the morning, on the other side of that luminary, 
the horns of the crescent are turned in the direction 
opposite to what they were at the former observa- 
tion, that is, they are turned toward the west. 
The luminous phase gradually increases in size, 
and assumes the form of a semicircle. Venus is 
then in its first quarter. In proportion as it 
advances toward the sun, the visible portion of its 
enlightened disc increases, and when it overtakes 
the sun it appears to us full. After it has passed 
by the sun, and appears in the west, its disc begins 
to be hollowed out, and the portion enlightened to 
us dimirushes, gradually passing through the same 
phases that it presented to us in its augmentation. 

These phenomena represent to us Venus as if it 
were a moon revolving round the sun and enlight- 
ened by its rays, and all observations show this to 
be the case. When Venus appears full, it is beyond 
the sun in respect to the earth, and its apparent 
diameter is then very small, not exceeding one 
sixth of a minute. On the contrary, as its disc 
diminishes, and its illuminated face turns more and 
more away from us, its apparent diameter increases. 
It must then be nearer to the earth. Finally, 
during the time elapsed between its disappearance 
in the evening and its reappearance in the morning, 
it may be seen, though rarely, to pass over the disc 
of the sun, looking like a round and black spot. 
It is then between the sun and earth, and its appa- 
rent diameter is greater than in any other part 
of its revolution, amounting to nearly one minute of 
a degree. 

These variations are not perceptible by the naked 
eye, because of the irradiation, which enlarges 
somewhat the apparent diameters of the heavenly 
bodies, and the more so the more illuminated they 
are. The phases of Venus increasing in size when 



154 



WONDERS OF THE HEAVENS 



it is beyond the sun, the increase of its light com- 
pensates for its greater distance. But the tele- 
scope destroys the illusion, and teaches us its real 
variations in distance by those of its apparent 
diameter. 

The orbit of Venus is not without that of the 
earth ; for if it were this planet would sometimes be 
seen in opposition to the sun, and the earth would 
be between them. This never happens. Nor is 
its orbit entirely beyond the sun in respect to the 
earth; if it were so, Venus would never be seen 
between the earth and sun — but it sometimes 
eclipses that luminary. In fine, while the sun 
seems to move in the ecliptic, Venus never removes 
beyond certain limits, and its oscillation about the 
sun, or its elongations, are always nearly of the same 
extent. These facts, united, evidently prove that 
Venus moves around the sun in an orbit returning 
into itself, and that it is carried onward with the 
sun by that body's apparent motion in the ecliptic. 

The progressive changes in the phases of that 
planet prove, moreover, that it is opaque, not 
shining by its own light, and that it is nearly 
spherical. 

The orbit of Venus, in its various positions, 
appearing to us under different points of view, there 
necessarily results quite a number of apparent 
irregularities and anomalies when we choose to 
refer its motions to the centre of the earth. But 
these complications in its movement disappear if we 
consider them in reference to the sun, which is the 
true centre of them. Observations confirm this 
statement. 

Venus is not the only planet that presents the 
phenomena of which we have thus spoken. Mer- 
cury exhibits perfectly similar appearances ; but its 
excursions are confined within narrower limits. 
This planet revolves around the sun like Venus, 
but in a smaller circle. The observation of its 
phases proves that it is opaque, being enlightened 
by the sun, and that it is nearly spherical. Its 
greatest apparent diameter is about eleven seconds, 
its least five seconds. 

These two planets (Mercury and Venus) are 
called inferior planets, because, the radius of their 



orbits being less than that of the earth's orbit, they 
are nearer than the earth is to the sun. To an 
observer on the earth, the motion of the planets 
appears sometimes direct, or fi-om west to east, 
sometimes retrograde, and both of these with great 
inequalities of velocity. Sometimes they appear 
stationary for a time, not sensibly changing their 
places in the sphere of the heavens. This diversity 
in their appearance is owing to the several com- 
binations of the motions of the planets and the earth 
in their orbits; and therefore, in order to give a full 
explanation, both these motions must be taken into 
the account. But it will not be amiss first to con- 
sider them separately. And since the earth is 
longer in going round the sun than either of the 
inferior planets, let us consider the earth as at rest 
in some part of its orbit, whilst an inferior planet 
(Mercury, for example) revolves round the sun, and 
see what its appearances would be on this suppo- 
sition. 

Whilst an inferior planet is moving in its supe- 
rior * semicircle, its motion, seen from the earth, is 
direct, or from west to east ; whilst moving in its 
inferior f semicircle, it is retrograde, or contrary to 
the order of the signs of the zodiac. When the 
earth is in the line of the nodes of an inferior planet, 
its orbit, in a perspective view, is represented by a 
straight line, because the plane of that orbit passes 
through the eye of an observer on the earth, and 
therefore the planet's apparent motion is in a straight 
line. Let the earth be in the line of Mercury's 
nodes, the projection of that planet's orbit is a 
straight line, extending on each side of the sun to 
the planet's greatest distance from that luminary. 
If Mercury at this time be in its superior semi- 
circle, its apparent motion is direct, but unequal, 
passing over unequal portions of the line in equal 
times, and the faster the nearer to the sun. If a 
conjunction happens, it passes behind the sun. 
But if, on the other hand, Mercury be in its infe- 
rior semicircle, its apparent motion is retrograde, 

* The superior semicircle is the part of the planet's orbit which is 
further from the earth than the sun is. 

t The inferior semicircle, that part which is nearer to the earth 
than the sun is. 



WONDERS OF THE HEAVENS. 



155 



in the same straight line, but more unequal than 
before, going the faster the nearer to the sun ; and 
in the case of a conjunction, passing between the 
sun and our eye, it appears on the sun's disc. The 
transits of Mercury are not unfrequent : those of 
Venus seldom happen, occurring but twice in one 
hundred and twenty years. When the earth is out 
of the line of the nodes of an inferior planet, its 
orbit appears an ellipse, more or less eccentric 
according as the eye is elevated above its plane. 
Suppose the earth ninety degrees out of the line of 
Mercury's nodes, the projection of its orbit will be 
an elliptic curve, and in superior conjunction it will 
be above the sun, and its motion direct — at inferior 
conjunction below the sun, and its motion retro- 
grade. In these cases its apparent motions will 
be unequal, faster the nearer conjunction, most 
unequal in the inferior semicircle, going through 
unequal arcs in equal times. 

Thus the geocentric motions of the inferior planets 
is sometimes swifter and sometimes slower, — swifter 
the nearer to the sun, slower the nearer to their 
greatest elongations. This inequality is not owing 
to the small real inequality of their motions in their 
orbits, but to their orbits being viewed obliquely, 
and, by this means, projected into long ellipses, or 
straight lines, with the sun in the middle of them ; 
in which projections a body moving with a uniform 
velocity round a circle will appear to move irregu- 
larly, swifter the nearer to the middle, slower the 
nearer to the extremities. 

An inferior planet is stationary while its motion 
is changing from direct to retrograde, or from retro- 
grade to direct ; that is, it will appear not to 
change its place sensibly for some time. If the earth 
stood still, the places where the planets were sta- 
tionary would be at their greatest elongations ; for, 
though it be the nature of a tangent to touch its 
circle only in one point, yet, when the circle is 
large, the receding of the curve from the tangent is 
not perceptible in the parts very near the point of 
contact. To an observer on the earth, the inferior 
planets appear always near the sun, alternately 
departing from and advancing towards it, first on 
one side and then on the other, sometimes so near 



the sun as to be rendered invisible by its strong 
light : sometimes, when in or near their nodes, they 
pass behind the sun, or between the earth and sun. 

We have thus far considered the earth as sta- 
tionary, while the inferior planets go round the sun. 
If the earth were really without motion, the places 
of the conjunctions, of the stations, of the direct and 
retrograde motions, of the planets, would always be 
in the same parts of the heavens. But the places 
where these appearances happen are continually 
advancing in the ecliptic, by the motion of the earth 
in its orbit. 

The geocentric motions of Venus are similar to 
those of Mercury, only, as Mercury goes through 
its orbit quicker than Venus, its changes are more 
frequent. 

An inferior planet in inferior conjunction with the 
sun is said to be in perigee, (nearest the earth,) in 
superior conjunction to be in apogee, (most distant 
from the earth.) These distances are, however, 
variable, and their variation is owing partly to the 
eccentricities of the planets' orbits, and partly to 
their motions, by which it happens that they are in 
perigee when in different parts of their orbits, as 
well as when the earth is in a different part of its 
orbit. Since the difference between the perihelion 
and aphelion distances is greater in the orbit of 
Mercury than in that of the earth. Mercury will be 
at its least possible distance from the earth when it 
is in perigee and at the same time in aphelion; 
because. Mercury being then between the earth and 
the sun, its attaining its greatest distance from the 
sun brings it nearer the earth. Again, Mercury is 
at its greatest possible distance from the earth 
when in apogee at the same time that it is in 
aphelion. With Venus it is not so, because the 
difference between its perihelion and aphelion dis- 
tances is less than that of the earth's. 

The inferior planets, revolving in orbits nearer 
the sun than the orbit of the earth, and being some- 
times nearer to us than at others, present apparent 
diameters sometimes greater than at others; and, 
conversely, from the difference of their apparent 
diameters, we might conclude that their distances 
were different. 



156 



WONDERS OF THE HEAVENS 



A common spectator may observe an inferior 
planet alternately approach nearer the sun till in 
conjunction, and recede further till at its greatest 
elongation ; and this will be first on one side of the 
sun and then on the other. But if we observe the 
change of its apparent place in the sphere of the 
heavens, its stations, direct motions, and retrogra- 
dations, and measure its disc frequently with the 



micrometer, we shall find that the planet at times 
comes nearer to us, and at others recedes further 
from us, in such a manner that, taking the whole 
of its apparent motion into account, its course round 
the earth appears to be a complicated curve ; and 
such a curve must it actually describe if the earth 
remain stationary. 

The plate below will best exhibit what the 




motions of Mercury must be if the earth has no 
real motion. The earth is placed in the centre, as 
it always appears to be. The curved and looped 
line, marked with the names of the months abbre- 
viated, shows the motion of Mercury, such as it 



appears to an observer on the earth, for seven suc- 
cessive years. The short strokes crossing the 
curved line show the place of the planet for aliquot 
parts of the month. The years, as well as the 
months, are set down in their proper places. Thus 



WONDERS OF THE HEAVENS. 



157 



the curve exhibits the direct motions, the stations, 
and retrogradations of Mercury, with the times of 
the same. It shows, also, its least and greatest dis- 
tances from the earth, with the several intermediate 
distances. The apparent motions of Venus are so 
similar to those of Mercury (the difference consist- 
ing in the less number of the loops) that it will be 
unnecessary to describe them. All the planets, 
except Mercury and Venus, come into conjunction 
and opposition with respect to the sun ; that is, at 
certain times they are in the same direction as the 
sun from the earth, and at other times in a contrary 
direction. But this last circumstance never happens 
to Mercury and Venus. We are led by other 
analogies, however, to examine if the other planets 
do not revolve about the sun like Mercury and 
Venus, but in larger orbits. By following out this 
idea, we perceive that the phenomena observed 
all declare the existence of such a motion. 

For example, take Mars. If we observe it with 
a telescope, we shall. see its disc constantly round 
(or nearly so) and enlightened ; it is never a 
crescent, like that of Venus. Yet it presents very 
perceptible variations in its apparent form. This 
form is completely circular in conjunction and 
opposition. In passing from one of these positions 
to the other, it contracts a little, and assumes the 
form of an oval, more or less narrow. This change 
always takes place in a slow and gradual manner. 

These phenomena teach us that Mars is an 
opaque body, and nearly spherical, reflecting the 
light of the sun. They are well represented by 
supposing this planet in motion in an orbit returning 
upon Itself, and surrounding the sun and earth. In 
fact, the connection of this circumstance with the 
phenomena exhibited, is so necessary that they 
cannot be true Mnthout its being equally so. If the 
orbit of Mars did not embrace that of the earth, it 
would never appear in opposition ; and if it did not 
surround the sun, so that it could at conjunction 
pass between the earth and sun, its disc would be- 
come a crescent, like those of Venus and the moon — 
instead of which it always appears nearly round. 

A superior planet, going round the sun in an 
orbit larger than the earth's, can only be in con- 



junction with the sun when the latter is between 
the earth and the planet. It is in opposition to the 
sun when the earth is between it and the sun, and 
in quadrature to the sun when its geocentric place 
differs ninety degrees from that of the sun. 

As the earth goes round the sun in less time and 
in a less orbit than any of the superior planets, it 
will not be amiss to suppose one of these last to 
stand still, in some part of its orbit, while the earth 
goes once round the sun, and to consider the appa- 
rent motions of the planet on this supposition. 
While the earth is in its most distant semicircle, 
the apparent motion of the planet would be direct ; 
while in its nearest semicircle, the planet's apparent 
motion would be retrograde ; and while the earth 
is near the points of contact of a line drawn from 
the planet tangent to the earth's orbit, the planet 
would appear stationary. 

The direct motion of a superior planet is swifter 
the nearer it is to conjunction, and slower the 
nearer it is to quadrature, with the sun ; and the 
retrograde motion is swifter the nearer the planet 
is to opposition, slower the nearer it is to quadra- 
ture. 

All the changes in the motions of the superior 
planets, caused by the earth's motion in its orbit, 
will happen in the same manner if we suppose the 
planet to go on slowly in its orbit, only they will 
happen every year when the earth is in a different 
part of its orbit, and, consequently, at different 
times of the year. 

A superior planet in conjunction with the sun is 
said to be in apogee : in opposition, it is said to be 
in perigee. 

The distance of each of the superior planets from 
the earth at apogee is variable, as is also their dis- 
tance at perigee. This variation is owing partly to 
the eccentricities of their orbits, and of the orbit of 
the earth, and partly to the motions of the planet 
and the earth ; by which it happens that they are in 
apogee or perigee when in different parts of their 
orbits, as well as when the earth is in a different 
part of its orbit. 

Since the superior planets go round the sun in 
orbits larger than that of the earth, they must be 



158 



WONDERS OF THE HEAVENS. 



sometimes nearer to us than they are at others, 
and, consequently, their apparent diameters are 
variable. " 

If we observe the apparent change of place of 
the superior planets in the sphere of the heavens, 
their direct motions, stations, and retrogradations, 
and measure their discs with the micrometer, we 



shall find, by the difference of their apparent diame- 
ters at different times, that their apparent courses 
are in complicated looped curves; and in such 
curves must their real motions be if the earth be 
fixed in the centre. In the figure, the motion of 
Mars during two years is laid down ; that of Jupiter 
for twelve years. 




The motions of the planets, as seen from the 
earth, being some of the most difficult appearances 
to represent to the imagination, we shall endeavor 
to illustrate them by ships in motion on the sea. 

A body moving along the same way with the 



eye, with a velocity equal to that of the eye, will 
appear to be at rest. Thus, if two ships are sailing 
eastward, in parallel lines, at the same rate, to a 
spectator in one of the ships the other will appear 
constantly in the same place, and he will have the 



WONDERS OF THE HEAVENS 



159 



same view of it as if both ships stood still. But if 
the body move with a greater velocity than the 
eye, it will appear to go forward, but with a less 
velocity than if the eye were at rest : if two ships 
sail, in parallel lines, eastward, with unequal 
velocities, the swifter v/ill, to a spectator in the 
slower ship, appear to sail eastward, but with a 
slower motion than if he stood on the land. A 
body moving the same way with the eye, but with 
a less velocity, will appear to move in a direction 
contrary to its real motion: if two ships sail east- 
ward with unequal velocities, to a spectator in the 
swifter ship the slower will appear to move west- 
ward. If a body move in a direction contrary to 
the motion of the eye, that body will seem to move 
in the direction of its real motion, but with a greater 
velocity than if the eye were at rest : if two ships 
sail, in parallel lines, one eastward, the other 
westward, to a spectator in the ship sailing east the 
other ship will appear to move west, but with a 
greater velocity than it really does. If a body at 
rest be viewed by the eye carried along, the body 
will appear to move with a velocity equal to that 
of the eye, but in a contrary direction : thus, to a 
spectator in a ship sailing eastward, the shore 
seems to go westward with a velocity equal to that 
of the ship. And if a body move round in one 
circle, and the eye be carried round in another 
concentric with the first, Avhen the eye and the 
body are in the semicircles on the same side, they 
may be considered as going in parallel lines in the 
same direction ; but when the eye and the moving 
"body are in opposite semicircles, they may be con- 
sidered as moving in parallel lines in opposite 
directions. In the figure, if two ships sail in the 
concentric circles abed, &c., and A B C D, &.C., 
according to the order of the letters, while they 
are in the curves ABC and ab c they may be con- 
sidered as moving eastward in the parallel lines 
A C and a c, and while in the semicircles D E F 
and def, as both going westward in the parallel 
D F and df. When the ships are in the opposite 
semicircles, ABC and c?e/, they may be considered 
as moving in parallels, but in different directions, 
one eastward in A C, and the other westward in df. 



By considering what has been said of the ships in 
motion, we hope the reader will be assisted in 
understanding the apparent motions of the planets. 




The apparent diameter of Mars increases in 
coming from conjunction to opposition, and dimin- 
ishes in going from opposition to conjunction. 
Therefore, in the first instance Mars must be 
approaching the earth, and in the second receding 
fi'om it. The variation of its apparent diameter is 
very considerable. Its greatest value is about 
eighteen seconds, its least about four seconds. 
The distances, then, are to each other as four to 
eighteen, or as four and a half nearly; thai is. 
Mars is nearly four and a half times more distant 
from the earth in the second case than in the first. 

These great differences teach us that the earth 
is not the centre of the motions of Mars. If we 
trust ourselves to the guidance of analogy, we shall 
find it most natural to conclude that this planet, like 
Mercury and Venus, revolves around the sun, which 
carries the orbit of Mars along with it in its annual 
motion through the ecliptic. The greatest and the 
least distances of Mars from the earth would happen 
when the sun was at its greatest distance from the 
earth. It would be at that time, therefore, we 
should find the apparent distance of that planet 
greatest or least ; and observing this, we are obliged 
to conclude that Mars revolves around the sun. 



160 



WONDERS OF THE HEAVENS 



The succession of phenomena that is presented 
by the other planets whose orbits include the 
earth's, and which, for that reason, are called 
superior planets, is precisely the same, and there- 
fore leads to the same conclusions ; only the varia- 
tions that the apparent form of their disc presents 
are much less perceptible, and that form varies less 
from a circle. This proves that their distances 
from the sun are much more considerable than that 
of Mars ; for if there were a planet placed so far 
from the sun that the sun's orbit could be regarded 
as a point in comparison to that distance, and this 
planet could be seen from the earth, the appear- 
ances presented to us would be the same as if we 
were at the sun's centre, and this planet revolved 
about us. Its disc would appear to us always as a 
circle, the variation of its phases being too small to 
be perceptible. 

We are led by these reflections to believe that 
the sun is placed near the centre of all the planet- 
ary orbits, and that it carries them along in its 
annual motion on the ecliptic. 

Shall we believe that this heavenly body really 
revolves in the ecliptic, or shall we regard this 
motion as an appearance produced by the real 
motion of the earth, which, carrying us successively 
to different points of the ecliptic, causes the sun, 
and the planetary orbits of which it is the centre, 
to appear to revolve about us 1 Assuredly, if we 
permit ourselves to be guided by analogy, always 
so evident in the works of God, we shall be led 
irresistibly to embrace the latter opinion, for in 
that, the sun being the common centre of our 
planetary system, symmetry will be established 
through all. 

Let us forget the earth, and, imagining ourselves 
at the centre of the sun, endeavor to consider our 
observations as made at that point. 

It first occurs to the mind as most simple to 
regard the planetary orbits as curves, whose planes 
pass through the centre of the sun. This suppo- 
sition is confirmed by the analogy existing between 
the motions of the planets round the sun, and those 
of the moon round the earth. We will examine if 
it agrees with observations. 



If the planets move in orbits whose planes pass 
through the centre of the sun, the points where 
each planet passes the plane of the ecliptic are 
opposite each other and in the same straight line, 
— a line drawn through the centre of the sun, and 
movable with it in the ecliptic. These points, 
then, determine the place where the orbit crosses 
the ecliptic, and the line joining them is called the 
line of the nodes. 

An observer at the sun might easily decide if 
this condition were fulfilled. He would determine, 
by a series of observations, the moments when the 
latitude of the planet was nothing, and he would 
calculate if, at the same moments, the heliocentric 
longitudes were the same, or if they differed by 
half a circumference. We can also determine, by 
observations from the earth, the moment when the 
planet passes its nodes ; but, not being at the cen- 
tre of the planetary motions, these nodes will not 
appear to be at opposite points on the celestial 
sphere, for the line that joins them, being carried 
by the sun along the ecliptic, will appear to us 
successively under different degrees of obliquity, 
and thus render the opposition imperceptible. 

Still, among all the situations which the plane of 
the orbit can assume, as regards us, there are two 
(very rarely happening, however,) in which the 
difficulty may be avoided. These are when the 
planet is without latitude, and at the same time in 
opposition to or conjunction with the sun ; for then 
we see it in the same right line as if we were at the 
centre of the sun. Many observations of this kind 
would decide if the node of the planet has always 
the same longitude seen from the sun. 

This method is quite practicable in regard to 
Mercury and Venus. As the revolutions of these 
two planets are very short, it follows that they 
must pass their nodes very often, as they must 
evidently pass through each in the course of every 
revolution. The frequency of these phenomena 
must therefore render the occurrence in question 
very frequent. The transit of these planets over 
the sun's disc is a particularly favorable opportunity 
for these observations ; for then we see them in 
the same right line, with the sun, while their lati- 



WONDERS OF THE HEAVENS. 



161 



tude is necessarily very small, and they are very 
near one of their nodes. The observation of these 
transits would then determine the constancy of the 
nodes as seen from the sun. 

All the observations of Mercury's transits unite 
to prove that this planet has a very small latitude, 
when its longitude, as seen from the sun, is about 
forty-five degrees. Consequently, it is then near 
that point which we call the descending node, because, 
when the planet passes it, it is descending toward 
the south pole of the ecliptic. This conclusion is 
confirmed by Delambre's calculation of the helio- 
centric longitude of Mercury's descending node at 
the transit in 1799. He found it, after applying 
certain necessary corrections, to be very nearly the 
same as the geocentric longitude given by the mean 
of the transits. Besides, its nodes are not strictly 
fixed. This will affect the results. Thus, by 
making such allowances as ought to be made in the 
calculation, we shall find that the longitude of the 
descending node of Mercury is nearly constant. 

The same constancy is noticeable in Mercury's 
passage through another point, called the ascending 
node, because the planet then is approaching the 
north pole of the ecliptic. 

The longitude, as seen from the sun, of the 
ascending node, exceeds that of the descending 
node by six signs nearly, that is, by a semicircum- 
ference. The two, then, as seen from the sun, are 
opposite each other, as they must be if all the 
points of the orbit be in the same plane. They are 
also nearly constant. 

The passages of Venus through its descending 
node present the same agreement. 

The agreement, however, of these phenomena, 

are not suflftcient to permit us to extend the same 

conclusion to the other planets, which, because of 

the slowness of their revolutions, are much more 

rarely to be seen with small latitude at the time of 

conjunction. We must therefore find some method 

that may prove the constancy of the node, without 

the necessity of observing it under circumstances 

so rare. Geometry furnishes, for this purpose, a 

method very general, as well as very simple, 

which, however, it is unnecessary to detail here. 
21 



In the present state of astronomy, the motions of 
the planets may be regarded as pretty accurately 
known. Observers of the present age are seeking 
to determine them with still greater exactness. 
Yet, in adopting the motions as they have been 
laid down, we may consider them as sufficiently 
accurate for our purpose. 

The place of the node being found, it may be 
used to determine the inclination. For this purpose, 
we observe when the sun is in the node of the planet, 
that is, when its longitude is the same as that of the 
node ; then we calculate, from observation, the 
planet's latitude as seen from the sun, and a trigo- 
nometrical calculation gives us the inclination of the 
plane of the orbit. 

It is difficult, or we might say impossible, to 
seize the exact moment when the sun is in that 
node ; but by observing both bodies many days in 
succession before and after the time of the sun's 
passage through the node, we may, by calculations 
founded on the results, determine quite accurately 
the moment when this phenomenon must have 
happened. Then we determine, for this moment, 
the respective positions of the two bodies, according 
to the law of the observed motions. From these 
positions we calculate the inclination of the orbit. 
This method, however, supposes the node already 
known. But if there still remains some small error 
in the element, it would have but a trifling effect 
upon the amount of the inclination; particularly if 
we select, for the observation of the phenomena, 
the times when the planet is near its quadrature. 

We ought to inform the reader, that all these 
isolated determinations of the elements of the orbit 
are but approximations, to be rectified afterward. 

When we determine the longitude of the nodes 
at times quite distant from each other, and refer 
the origin of these longitudes to the same point of 
the ecliptic, having regard to the motion of the 
equinoxes, we find that the nodes are not fixed. 
They all have retrograde motions on the ecliptic, 
that is, in a direction contrary to the propet motion 
of the planet. These variations are very slow, 
and of the nature of those which are called secular. 
The inclinations of the diflferent orbits also experi- 



162 



WONDERS OF THE HEAVENS 



ence some variations in regard to each other and 
to the ecliptic. 

The retrogradation of the nodes of the lunar and 
planetary orbits is a necessary consequence of 
universal attraction. The same is true in respect 
to the variations of inclination. 

Analysis, besides making known this connection, 
has enabled us to calculate their effects. 

The position of the plane of the orbit being 
determined, it remains to find the law of the planet's 
motions, and the form of the curve that it describes. 
Each of these would be known if we could deter- 
mine for every instant the length of the radius 
vector, (i. e. the line drawn from the sun's to the 
planet's centre,) and the angle formed by this radius 
with a fixed right line drawn in the plane of the 
orbit and passing through the centre of the sun. 

The first element to be determined is the length 
of a complete sidereal revolution of the planet round 
the sun. To discover this, the most simple and 
direct method is to observe the interval of time 
between two successive passages of the planet 
through the same node. As the plane of the 
ecliptic moves slowly in the heavens, it will be 
necessary to make allowance for this motion during 
the time elapsed between the observations com- 
pared, that is, it will be necessary to reduce them 
to a fixed ecliptic. 

As we must be prepared to find disturbances in 
the motions of the planets, so we can greatly dimin- 
ish their effect by deducing the mean motions from 
observations which comprehend a great number of 
revolutions, in order that, the periodic inequalities 
being compensated several times in the interval, 
the error which remains in the final result may be 
inappreciable by a division among so many revolu- 
tions. In this manner was determined the length 
of the mean year, independently of the periodic 
inequalities in the sun's motion. 

The mean motion being known, we must next 
deduce from observation the angular motion of the 
planet round the sun, and the variations of its dis- 
tance from that luminary. For this purpose, con- 
junctions and oppositions are extremely favora- 
ble. In fact, under these circumstances, the radius 



vector drawn from the earth to the planet, and that 
which is drawn to it fi:"om the sun's centre, are pro- 
jected upon the plane of the ecliptic in the same 
right line. Thus the point of the ecliptic to which 
we refer the planet is either the same as that to 
which an observer at the sun's centre would refer 
it, or it is directly opposite. In these two cases 
the longitude of the planet as seen from the sun, 
(heliocentric,) is derived from its longitude as seen 
from the earth, (geocentric;) for in conjunctions 
these two are equal to each other; in oppositions 
they differ by two right angles, (or one hundred 
and eighty degrees.) And as the position of the 
orbit upon the plane of the ecliptic is known, and 
that of the planet's node, we can determine by 
calculation the distance of the planet from its node, 
and the distance of the planet from the sun, 
expressed in parts of the earth's distance from the 
sun. 

The oppositions and conjunctions of the planets 
happen successively in different points of the hea- 
vens ; and they do not always correspond to the 
same points of their orbits. Thus, making many 
similar observations, we shall find successively 
different angles and different radii vectores. Then 
we can measure these radii, place them around the 
sun in their true positions, and trace, by means of 
them, the form of the curve which the planet de- 
scribes. In order to obtain these results, it is not 
even necessary that the planet be observed at the 
time of its opposition and conjunction. One geo- 
centric longitude and latitude, observed at any 
time, will suffice, with the aid of calculation, to 
find the radius vector and the planet's distance from 
its node. 

The curve traced in this way for each of the 
planets is very similar to an ellipse, having the sun 
in one of its foci. Analogy induces us to examine 
if the laws of elliptic motion will not agree with the 
conclusions to which observation leads us. 

The method of proof is very simple. Three 
points, given in position on a plane, will be sufficient 
to determine satisfactorily an ellipse, one of whose 
foci is known. If, therefore, we find an ellipse 
which satisfies three observations of the planet, we 



WONDERS OF THE HEAVENS 



163 



must examine whether it satisfies all other observa- 
tions that may be or have been made. 

In this manner it has been found that the orbits 
of all the planets are ellipses, with the sun in one of 
their foci. Around this point the radii vectores describe 
equal areas in equal times. These are the first and 
second laws of Kepler; so called because they were 
discovered by that great astronomer. 

The eccentricities of the planetary ellipses expe- 
rience small variations in a long course of time. 
Theory teaches us the laws and the extent of these 
changes. Those of Mercury, Mars, and Jupiter, 
at present, are increasing ; those of the other plan- 
ets are diminishing. 

The perihelia of the planets are not fixed un- 
changeably in the heavens. They move slowly in 
the planes of the orbits. 

For all the planets, except Venus, these motions 
are direct, (that is, from west to east.) But the 
perihelion of Venus moves from east to west, or 
retrograde. Exact observations are, as yet, too few 
and recent to determine with precision the amount 
of these small variations. The theory of attraction 
determines it with much greater nicety. 

To know the absolute quantity of these motions, 
and their direction, we refer them not to the equi- 
noxes, which are movable, but to some point on 
the ecliptic that is fixed and determined. 

The knowledge of the elliptic motions of the 
planets depends on seven elements for each of 
them. Two serve to determine the position of the 
orbit : these are the inclination of the orbit, and the 
longitude of the node. The others relate to the 
motion in the ellipse : these are the length of the 
sidereal revolution; half the greater axis of the 
orbit, or the mean distance of the planet from the 
sun ; the eccentricity ; the mean longitude of the 
planet at a given time ; the longitude of its peri- 
helion at the same time. As there are eleven 
planets known at present, it is necessary to have 
seventy-seven elements determined, before we can 
have a complete knowledge of our planetary system 
in the present state of astronom3\ 

Although the determination of these elements 
may be made, and has been made by the above- 



described procedure, it is very evident that, being 
applied to each element separately and successively, 
it could furnish only approximations. Astronomers 
of the present day are sufficiently advanced in that 
science, and have reflected on the causes that affect 
the accuracy of calculations long enough, to per- 
ceive the necessity of considering all the elements 
simultaneously, if they would estimate their mutual 
influences in the disturbances they experience. We 
must determine their amounts, not by a single 
observation, but by many, if we would perfect the 
calculations, and give the stamp of accuracy to our 
first approximations. 

Those planets move the slowest, that are most 
distant from the sun. By comparing their veloci- 
ties with their distances, Kepler discovered this 
remarkable relation : — The squares of the times of 
their revolutions are as the cubes of their mean distances. 
This is called Kepler's third law. 

This law, being shown to be true as respects all 
the planets, ought to be regarded as more exact 
than observation itself. Wherefore, instead of de- 
riving from observation the ratios of the planets' 
distances from the sun, (ratios always difficult to 
find with accuracy,) it is better to deduce them, by 
this law, from the length of their sidereal revolu- 
tions, for we can measure these last with the 
greatest precision, from the returns of each planet 
to the same node. Reciprocally, if we knew the 
planet's distance from the sun, but did not know 
the time of its sidereal revolution, we might calcu- 
late the latter by means of the same law. 

This is the case with regard to the newly-dis- 
covered planets ; for observation enabled astrono- 
mers to determine their greater axes, and all the 
elements of their orbits, long before they had 
finished a sidereal revolution. 

The earth is also subject to this law, like all the 
other planets. If we admit its annual motion, the 
orbit becomes that of a planet revolving round the 
sun, conformably to Kepler's laws. The time of 
its revolution, calculated from its solar distance, 
according to this theory, is exactly equal to a 
sidereal year. 

This fact shows that there is a striking analogy 



164 



WONDERS OF THE HEAVENS 



between the earth and the other planetary bodies. 
The motion of our globe, imperceptible to the 
senses, could not have been indicated to us in a 
more decided manner. 

Kepler's laws are the foundation of all theoretic 
astronomy. They conduct us to the laAv of universal 
gravitation, which is a consequence of them. 

The motions of the planets are not made exactly 
in ellipses. They are subject to a great number of 
minute irregularities, which observation and theory 
have discovered and determined with much accu- 
racy. 

The most considerable changes are those which 
affect the motions of Jupiter and Saturn. On com- 
paring modern and ancient observations, a diminu- 
tion in the time of Jupiter's revolution, and an 
increase in that of Saturn's, is detected. Modern 
observations compared with each other give a con- 
trary result. These variations indicate in the 
motions of these planets great inequalities, whose 
periods are very long and whose effect upon the 
two planets is opposite, so that the motion of the 
one increases, while that of the other is retarded. 
These phenomena have been completely developed 
by La Place, who has made known their laws and 
given to the tables of Jupiter and Saturn an unex- 
pected degree of accuracy. 

It is quite remarkable that the distance from the 
sun of the four smallest planets, (Ceres, Pallas, 
Vesta, Juno,) are almost exactly the same. From 
this results the slight difference in the times of their 
sidereal revolutions, which are deduced from their 
distances by the third law of Kepler. This equali- 
ty is particularly striking as respects Ceres and 
Pallas. Ceres and Juno, though they differ more 
in their distances, agree almost exactly in their 
eccentricities, and in the position of their nodes. 
From these facts, some astronomers have imagined 
that these four might have been formerly united, 
forming a large planet, which was separated by the 
effect of some internal explosions, — a theory, which, 
however incredible it may seem, has (to say the 
least) some plausible arguments in its favor. With 
these we may furnish the reader before closing this 
treatise. 



When we wish to make observations on the 
motions of the planets, it is often essential that we 
should know the time they occupy in returning to 
the same situation with respect to the sun. This is 
called their synodic revolution. 

We may deduce this from the preceding results. 
It is sufficient that we rely upon the general fact, 
that all the known planets make their revolutions 
in the same direction, that is, from west to east, a 
conformity which is one of the most remarkable 
phenomena of the solar system. 

If we find the difference between the daily motion 
of the earth and that of any other planet, this 
difference will express the quantity by which the 
two planets, seen from the sun, remove from each 
in the course of twenty-four hours ; and, supposing 
their motion uniform, we can deduce from it, by a 
simple proportion, the number of days necessary 
for their attaining a distance from each other of 
three hundred and sixty degrees, that is, for their 
arriving again at the same relative position in their 
revolution round the sun, which is the time of the 
planet's synodic revolution. 

By comparing the mean motion of the planets 
with the mean motion of the sun, we can calculate 
the time at which these bodies ought to be found 
again in the same position with regard to the 
earth. These periods differ from those of a synodic 
revolution, which only bring the planet to the same 
angular distance from the sun. It is useful to know 
them, because, at these epochs, the hours of the 
rising, meridian transits, and setting of the planets, 
and all the inequalities that affect their motions, 
are found nearly the same as at the preceding 
epoch ; so that the phenomena that depend on the 
position of these bodies begin again, and take place 
in the same order, affording an easy method of 
predicting them. 

We may, therefore, know all the times of the 
mean conjunctions of Mercury with the sun, which 
are phenomena very important to be observed. 

If the orbit of Mercury were wholly in the plane 
of the earth's orbit, the former planet, in each of 
its inferior conjunctions, would transit the sun's 
disc. But the inclination of the planet's orbit pre- 



WONDERS OF THE HEAVENS. 



165 



vents the frequent return of these phenomena, and 
they are less frequent than conjunctions. 

It is evident, indeed, that Mercury at conjunc- 
tion cannot be projected on the sun's disc, except 
when its latitude, as observed from the earth, is 
less than the sun's apparent semidiameter. In 
every other case it passes above or below the sun. 

Many circumstances operate against the fulfil- 
ment of this condition, and cause a variation in the 
times of Mercury's transits over the sun. Among 
these may be reckoned the great eccentricity of 
that planet's orbit, which renders its motion very 
unequal ; the motion of the nodes, which prevents 
the planet from having the same latitude when it 
returns to the same conjunction ; and, above all, the 
annual motion of the orbit, which, being carried 
forward on the ecliptic by the sun, appears under 
different elongations and aspects, whence result 
considerable variations in the geocentric latitude of 
that planet. 

In the midst of so many inequalities, the only 
method that is left us of predicting accurately all 
the transits, consists in finding the epochs when 
they may take place, and then calculating by the 
tables all the conjunctions corresponding to these 
epochs, to determine those in which the transits 
will really happen. Tables have been formed in 
this way, which contain the transits that have 
happened, and those that will happen during several 
centuries. 

We can find in these tables the effect of the 
different periods which have been ascertained. 
They also show that the transits of Mercury always 
take place in May or November. They are much 
more frequent in the latter month, owing to the 
position of Mercury's ellipse on the plane of the 
ecliptic. This ellipse is at present situated in such 
a way, that its perihelion is toward us in winter, 
its aphelion in summer; and, as the orbit is very 
eccentric. Mercury is much nearer the sun in the 
month of November than in the month of May. 
And if we imagine a luminous cone, formed by 
visual rays drawn from any point of the earth's 
surface to the sun, this cone, having for its vertex 
a point on the earth, and for its base the sun's disc, 



will be the more likely to be met by Mercury the 
nearer that planet is to the sun, and consequently 
the transits will be most frequent in the autumn. 
The preceding considerations, and the methods 
with which they furnish us, apply also to the orbit 
of Venus. 

The transits of Venus over the sun's disc are 
much more rare thaft those of Mercury, because 
Venus is much more distant from that luminary. 

Venus is sometimes visible to the naked eye in 
broad daylight. This remarkable phenomenon takes 
place when the planet is in a position to reflect to 
us the most rays. But the phases of Venus increase 
in extent, as the planet departs from the earth. 
This tends to increase its splendor, while the 
increase of distance tends to diminish it, for the 
intensity of rays of light diminishes in proportion to 
the square of the distance. There is a middle 
point at which the planet will appear to us most 
brilliant. The time elapsed between the returns 
of Venus to this situation is about eight years ; but 
in many other, positions Venus may be seen at 
noonday, and this phenomenon happens frequently. 



SECTION II. 

Individual planets — Mercury — Period of its reA'olution — Method of 
finding its rotation — Motion in its orbit per hour — When visible — 
Its diameter and distance from the sun — Its telescopic appearances 
— Its mountains — Its atmosphere — Venus — Its distance from the 
sun, diameter, and rate of motion — Its period — Inclination of its 
orbit — Telescopic appearances — Atmosphere — Rotation — Moun- 
tains — Mars — How the earth and moon appear there — Its irregulari- 
ties, the subject of Kepler's studies— Peculiarities in its appear- 
ance — Efiects of its atmosphere on the color of the planet — Its 
luminous zone, and the cause of the same — Mars supposed phos- 
phorescent — Ultra zodiacal planets — Seemingly disturb the har- 
mony of the system — Their feeble powers of gravitation — Pecu- 
liarities of Ceres — of Pallas — of Juno — of Vesta — Olber's theory 
respecting the small planets. 

We have purposely delayed, thus far, to speak 
of the planets individually, in order that their 
general relations might be presented in an uncon- 
fused manjier, and that we might devote some 
pages to a separate consideration of their physical 



tssaasiEa^iaaa 



166 



WONDERS OF THE HEAVENS 



constitutions, and to the varieties in their appear- 
ance and condition. 

Very careful observations have been made to 
discover spots on the discs of the planets, in order 
to determine whether, like the sun, they have a 
motion of rotation. Such a motion has been found 
to exist with respect to all those upon which spots 
have been discovered. These are Venus, Mars, 
Jupiter, and Saturn. The method is the same as 
for the sun and moon. It has been proved, by 
another method, that Mercury also turns on its axis. 

MERCURY 

Is the nearest planet to the sun, and goes round 
it in a little less than eighty-eight of our days, or 
one fourth of our year nearly. But being seldom 
seen^ and no spots appearing on its surface, (it being 
so enveloped in the sun's rays that nothing can be 
perceived but a sparkling disc of light,) some other 
method was necessary to reveal to us that it re- 
volved on its axis. The method used by Schroeter 
was a continued observation of the variation in the 
horns of the planet. In its course round the sun, it 
moves at the rate of one hundred and fifty thou- 
sand miles an hour. Its light and heat from the sun 
are nearly seven times as great as ours ; and the sun 
appears to its inhabitants nearly seven times as 
large as to us. Yet the great heat is not a sufficient 
argument against its being habitable; since the 
Creator could as easily suit the constitutions of its 
inhabitants to the heat of their planet, as ours to 
that of the earth. And it is probable that the 
inhabitants of that planet think the same of us as 
we do of the people of Jupiter, Saturn, and Herschel, 
viz. that we must be in a melancholy condition, 
suffer intolerable cold, and be poor, benighted souls, 
at such a distance from the sun. Mercury appears 
to us with all the various phases of the moon, when 
viewed, at different times, through a good telescope, 
except that it never appears quite full, because its 
enlightened side is turned directly toward us only 
when it is so near the sun as to be lost from 
our view in his beams. As its enlightened side is 
always toward the sun, it evidently shines by no 
light of its own, for if it did it would constantly 



appear round. That it moves round the sun in an 
orbit within the earth's is also plain, because it is 
never seen opposite the sun, nor more than fifty- 
four times the sun's breadth from his centre. Its 
orbit is inclined seven degrees to the ecliptic, and 
that node, from which it ascends northward, is in 
the fourteenth degree of " the Bull," the opposite 
in the fourteenth degree of "the Scorpion." The 
earth is in these points on the sixth of November 
and the fourth of May, and when Mercury comes to 
either of its nodes at inferior conjunction about 
these times, it will appear to pass over the sun's 
disc like a round dark spot. But in all other parts 
of its orbit the conjunctions are invisible, because 
it goes either above or below the sun. 

When this planet becomes visible, it remains so 
only a few successive evenings or mornings, because 
of the rapidity of its daily motion. When it begins 
to appear in the evening, it is with difficulty dis- 
tinguished in the rays of twilight. It disengages 
itself more and more the following days, and, after 
having departed nearly twenty-three degrees from 
the sun, it returns toward him again. In this in- 
terval, its motion with respect to the stars is direct ; 
but when in returning it comes within eighteen 
degrees of the sun, it seems stationary, after which 
its motion appears retrograde. It continues to 
approach the sun, and is again lost in his rays in 
the evening. After continuing invisible for some 
time, it is seen again in the morning disengaging 
itself from the sun's rays, and receding from the 
sun, its motion being still retrograde as before its 
disappearance. Arriving at the distance of eigh- 
teen degrees, it is again stationary ; then resumes its 
direct motion, till its distance amounts to twenty- 
two and a half degrees; then it returns, and, dis- 
appearing in the light of the dawn, is soon after 
seen again in the evening, producing the same 
phenomena as before. 

The best time to see Mercury in the evening is 
in spring, at the time the planet is east of the sun, 
and at its greatest distance from that body. It 
will then be visible for several minutes, and will 
set about an hour and fifty minutes after the sun. 
But if the planet is west of the sun, and at its 



WONDERS OF THE HEAVENS 



167 



greatest distance, it will rise about one hour and 
fifty minutes before that body, and will be most 
advantageously seen in the morning at the latter 
part of summer or the beginning of autumn. 

The planet Mercury is about three thousand 
one hundred and fifty miles in diameter, and re- 
volves round the sun at the distance of thirty-seven 
millions of miles. It emits a brilliant white light, 
and twinkles like the fixed stars. The dazzling 
splendor of its rays, the shortness of the interval 
during which observations can be made upon its 
disc, and its proximity to the vapors of the horizon 
when it is observed, have prevented astronomers 
from making any interesting discoveries respecting 
this planet. When Mercury is viewed with a 
telescope of high magnifying power, it exhibits 
nearly the same phases as the moon does, being 
sometimes horned, and sometimes nearly full. Dr. 
Herschel frequently examined Mercury with tele- 
scopes magnifying two hundred and three hundred 
times; but it always appeared equally luminous in 
every part of its disc, without any dark spot or 
ragged edge. Schroeter was more successful. He 
maintains that he has seen, not only spots, but even 
mountains, in Mercury; and that he succeeded in 
measuring the altitude of two of them. One of 
these mountains was about a mile and a fifth in 
height, the other ten miles and three quarters, 
which last is nearly three times as high as Chimbo- 
razo, one of the highest mountains on the earth. 
The highest mountains are situated in its southern 
hemisphere. By examining the variation in the 
daily appearance of Mercury's horns, Schroeter 
found the period of its diurnal rotation about its 
axis to be twenty-four hours, five minutes, twenty- 
eight seconds. Wallot imagined that Mercury had 
a horizontal refraction of two hundred and seventy- 
six seconds; but Bugge, when observing th&transit 
of this planet in 1802, could perceive no traces of 
an atmosphere. 

VENUS. 

Venus is computed to be sixty-eight millions of 
miles from the sun, and goes round in its orbit in 
about two hundred and twenty-four days and seven- 



teen hours of our time, moving at the rate of 
seventy-six thousand miles an hour. According to 
Bianchini's observations, its day is as long as twen- 
ty-four and one third of our days. This however is 
probably an error, as we shall see hereafter. Its 
diameter is seven thousand seven hundred miles. 

Its orbit includes that of Mercury within it ; for, 
at its greatest elongation, or apparent distance from 
the sun, it is ninety-six times his breadth from his 
centre, which is almost double the distance of 
Mercury. Its orbit is included by the earth's, for, if 
it were not, it might be seen as often in opposition 
to the sun, as it is in conjunction with him ; but it 
was never seen ninety degrees, or a fourth part of 
a circle, from the sun. 

When Venus appears west of the sun, it rises 
before him in the morning, and is called the morn- 
ing star; when it appears east of the sun, it shines 
in the evening after he sets, and is then called the 
eveni?ig star; being each, in turn, for two hundred 
and ninety days. It may perhaps be surprising, at 
first, that Venus should keep longer on the east or 
west of the sun than the whole time of its period 
round him. But the difficulty vanishes when we 
consider that the earth is all the while going round 
the sun the same way, though not so quick, as 
Venus ; and therefore its relative motion to the 
earth must in every period be as much slower than 
its absolute motion in its orbit, as the earth during 
that time advances forward in the ecliptic, which 
is two hundred and twenty degrees. To us Venus 
appears, through a telescope, with all the various 
shapes of the moon. 

Venus's orbit is inclined three and a half degrees 
to the earth's, and crosses it in Gemini and Sagit- 
tarius; and, therefore, when the earth is about 
these points of the ecliptic at the time that Venus 
is in its inferior conjunction, it will appear like a 
spot on the sun, and afford a more certain method 
of finding the distances of all the planets from the 
sun, than any other yet known. But these appear- 
ances happen very seldom. Excepting such transits 
as these, this planet shows the same appearances to 
us regularly every eight years, its conjunctions, 
elongations, and times of rising and setting, being 



WMMI ■tlllT-nnmi.--J.r'.^;n^-jT 



168 



WONDERS OF THE HEAVENS 



very nearly the same, on the same days, as 
before. 

The powerful telescopes of Herschel and Schroeter 
were employed in examining the various appear- 
ances of this planet. On the nineteenth of June, 
1780, Herschel observed spots on its surface, as 




represented in the figure : a c? c is a bluish spot, and 
ceb Q. brighter spot. They met in an angle at a 
point c, distant from the cusp a about one third of 
the planet's diameter. This astronomer also ob- 
served that Venus was much brighter round its 
limb than in that part which separates the enlight- 
ened from the obscure portion of the disc. As this 
brightness round its limb diminishes pretty sud- 
denly, it resembles a narrow, luminous border, and 
therefore does not seem to be the result of any 
optical deception. The light seemed to decrease 
gradually between this border and the boundary of 
the illuminated part of the planet's disc. Schroeter 
had before observed that the light appeared strong- 
est at the outward limb, whence it decreased 
gradually, and in a regular progression, toward the 
interior edge ; but he differed from Herschel with 
regard to the sudden diminution of this marginal 
light. Herschel ascribed the appearance to the 
atmosphere of Venus, which, like our own, is proba- 
bly replete with matter that reflects and refracts 
light copiously in all directions. Therefore, on the 
border, where we have an oblique view of it, there 
will be an increase of this luminous appearance. 
Herschel considered the real surface of Venus to be 
less luminous than its atmosphere, and this accounts 
for the small number of visible spots on its disc; 
for the planet will commonly be enveloped by its 



dense atmosphere, so as not to present us with any 
variety of appearances. This also shows the reason 
why the spots, when there are any visible, seem 
generally darker than the rest of the body. The 
observations of this astronomer did not enable him 
to ascertain the diurnal rotation or the position of 
the axis of the planet ; but he was of opinion that it 
could not be so slow as twenty-four days, the period 
assigned by Bianchini, 

The atmosphere of Venus appears to be very 
dense, not merely from the changes which take 
place- in the dark spots, but, as Schroeter inferred, 
from the illumination of its cusps when it is near 
its inferior conjunctions, vi^hen the enlightened ends 
of its horns reach far beyond a semicircle. 

This astronomer's observations led him to some 
results different from Herschel's. He discovered 
several mountains, and found that, like those of the 
moon, they were always highest in the southern 
hemisphere, their perpendicular height being near- 
ly as the diameters of their respective planets. 
From the eleventh of December, 1789, to the 




eleventh of January, 1790, the southern horn b of 
Venus appeared much blunted, with an enlightened 
mountain m in the dark hemisphere near twenty- 
two miles high. 

In order to deterrnine the time of the planet's 
rotation, Schroeter observed the different shapes of 
the horns. Their appearance generally varied in 
a few hours, and became nearly the same again 
about half an hour sooner each day. Hence he 
concluded that its period of rotation must be about 
twenty-three and a half hours, that its equator is 



WONDERS OF THE HEAVENS 



169 



considerably inclined to the ecliptic, and the pole 
at a considerable distance from the point of the 
horn. On the thirtieth of December, 1791, at eight 
o'clock in the morning, the southern horn appeared 
with the same bluntness, and with the same enlight- 
ened mountain in the dark hemisphere, as it had 
done on the twenty-eighth of December, 1789, at 
five o'clock in the morning. Hence the period of 
Venus's rotation must be twenty-three hours, 
twenty minutes, fifty-nine seconds — only about one 
minute less than the time given by Cassini. The 
alternate bluntness and sharpness of the horns, of 
this planet, Schroeter supposes to arise from the 
shadow of a high mountain. The appearance of 
Venus, with its ragged edge, and blunt horn, is 
shown in the figures. 




The luminous margin, which we have already 
mentioned, induced Schroeter to believe that Venus 
had an atmosphere of considerable extent. At the 
interior edge, the light becomes dim till it loses 
itself in a faint bluish gray, and forms a ragged 
margin, (as in the above plate,) which it is difficult 
to perceive even with the best telescopes. This 
diminution of light is much more sensible near the 
middle d than at the cusps a, 6. 

On the ninth of September, 1790, he observed 
that the southern cusp disappeared, and was bent, 
like a hook, about eight seconds beyond the lumi- 
nous semicircle into the dark hemisphere. The 
northern cusp had the same tapering termination, 
but did not encroach upon the dark part of the disc. 

A streak, however, of the glimmering bluish light 

22 



proceeded about eight seconds along the dark limb, 
from the point of the cusp b to c, (figure above,) 
b being the extremity of the diameter a b, and con- 
sequently the natural termination of the cusp. 
The streak b c, verging to a pale gray, was faint 
when compared with the light of the cusp at b. 
Schroeter considered this appearance as the twi- 
light of Venus. " That it is a real twilight is evident 
from the relative appearances of the cusps." On 
the ninth and twelfth of March, 1790, when the 
southern cusp extended in a hooked direction into 
the dark hemisphere, the pale blue light appeared 
only at the point of the northern cusp, and pro- 
ceeded in a spherical curve into the dark part. On 
the tenth of March, when the southern cusp did 
not proceed so far, the pale streak was perceptible 
at poth points, but more sensible at the northern. 
The bright prolongation of the southern cusp on 
the tenth and twelfth of March, must be ascribed to 
the solar light on a ridge of mountains, whence it 
could not be strictly spherical. When the bright 
prolongation was not considerable, twilight had its 
due effect, and the true spherical arc of the dark 
limb appeared faintly illuminated. From these 
observations, Schroeter calculated that the de?ise 
part of Venus's atmosphere is about sixteen thou- 
sand feet, or over three miles, high ; and he con- 
cluded, that its upper strata must be far above the 
highest mountains, that the atmosphere is more 
opaque than that of the moon, and that its density 




is a sufficient reason why we do not discover, on 
the surface of the planet, those shades and varieties 



170 



WONDERS OF THE HEAVENS 



of appearance which are to be seen on the other 
planets. 

The preceding plate represents Venus as seen by 
Bianchini. 

MARS. 

This planet is the next to the earth in the order 
of distance from the sun, which distance is equal to 
one hundred and forty-four millions of miles. It 
moves at the rate of fifty-five thousand miles an 
hour, and goes through its orbit in one year and 
ten months of our time, which is of course the length 
of its year. The time of its rotation (or length of 
its day) is twenty-four hours and forty minutes. 
Its diameter is four thousand one hundred miles. 
The quantity of light and heat at Mars is but one 
half as much as ours, if we consider their amount 
as wholly depending on the sun. That luminary 
appears but half as large at Mars as at the earth. 
Mars is much smaller than the earth, and if any 
moon attends it, it must be very small, since the 
most powerful telescopes have been repeatedly 
directed that way for the purpose of making such 
a discovery, but without success. 

To the inhabitants of Mars, the earth and the 
moon must appear like two moons, changing places 
continually Avith each other, and appearing some- 
times horned, sometimes half and sometimes three 
quarters enlightened, but never full, and never 
more than a quarter of a degree asunder. 

The earth must appear to Mars about as large 
as Venus does to us. It can never be seen more 
than forty-eight degrees from the sun, and some- 
times passes over the sun's disc, as do also Mercury 
and Venus. But Mercury cannot be seen there by 
such eyes as ours, unaided by instruments, and 
Venus will be seen as seldom as we see Mercury. 
Jupiter and Saturn are as visible to Mars as to us. 
The axis of Mars is inclined thirty degrees eighteen 
minutes, and the plane of its orbit about two 
degrees, to the plane of the ecliptic. 

At its nearest approach to the earth its distance 
from us is about fifty millions of miles, and its great- 
est distance is about two hundred and forty millions 
of miles; so that in the former case, it appears 



tAventy-five times larger than in the latter. To an 
observer in this planet, the earth will appear alter- 
nately as a morning and evening star, and will ex- 
hibit all the phases of the moon, just as Venus does 
to us, but with a less degree of apparent magnitude 
and splendor. 

The irregularities of Mars in its orbit being the 
most considerable of all the primary planets, Kepler 
fixed upon it as the first object of his investigations 
respecting the nature of the planetary orbits ; and, 
after extraordinary labor, he at last discovered 
that the orbit of this planet is elliptical, that the 
sun is situated in one of the foci of the ellipse, and 
that there is no point round which the angular 
motion is uniform. In the pursuit of this inquiry, 
he found the same true as to the earth's orbit ; and 
it was reasonable to conclude from analogy that 
all the planetary orbits are elliptical, having the 
sun in one of their foci. 

Continued observations show that the figure of 
Mars is not an exact sphere, but an oblate spheroid, 
whose polar diameter is to its equatorial as fifteen 
to sixteen nearly. The planet Mars is remarkable 
for the redness of its light, the brightness of its 
polar regions, and the variety of spots on its 
surface. The atmosphere of this planet, which 
astronomers have long considered as of an extraor- 
dinary extent and density, is the cause of the 
remarkable redness of its light. When a beam of 
white light passes through any medium, its color 
inclines to red, in proportion to the density of the 
medium, and the space through which it has trav- 
elled. The momentum of the red (or least refrangi- 
ble) rays being greater than that of the violet (or 
most refrangible) rays, the former will make their 
way through the resisting medium, while the latter 
are either reflected or absorbed. The color of the 
beam, therefore, when it reaches the eye, must 
partake of the color of the least refrangible rays, 
and this color must increase with the number of the 
violet rays that have been obstructed. Hence we 
see that the morning and evening clouds are beau- 
tifully tinged with red; that the sun, moon, and 
stars, appear of the same color when near the 
horizon; and that every luminous object seen 



bewi 



WONDERS OF THE HEAVENS 



171 



through a dry mist is of a ruddy hue. The planet 
Mars has an atmosphere of great density and 
extent, as is evident from the dim appearance of 
fixed stars, even at a distance from its disc. 
Cassini observed a star in the constellation of the 
Water-Bearer, which, at the distance of a tenth of a 
degree from the disc, became so faint as to be in- 
visible even with a telescope of three feet. The 
same phenomenon was observed at Paris by Roemer. 
The dim light, therefore, by which Mars is illumi- 
nated, having to pass twice through its atmosphere 
before it reaches the earth, must be deprived of a 
great proportion of its violet rays, and consequently 
the color of the resulting light, by which Mars is 
visible, must be red. As there is a considerable 
difference of color among the other planets, and 
likewise among the fixed stars, are we not entitled 
to conclude that those in which the red color pre- 
dominates are surrounded with the most extensive, 
or the densest, atmosphere? According to this 
principle, the atmosphere of Saturn must be the 
next to that of Mars in density or extent. 

After Galileo had discovered the phases of Mars, 
Dr. Hook and Cassini discovered upon the disc of 
this planet a number of dark spots. Hook perceived 
some trifling changes in their position, but Cassini 
had the merit of determining from these changes 
that the diurnal revolution of the planet was per- 
formed in twenty-four hours and forty minutes. 

The luminous zone at the southern pole of 
Mars, which had before been often noticed by 
astronomers, was particularly observed by Maraldi. 
During six month's observations he found it subject 
to many changes. Sometimes it appeared bright, 
at other times faint, and, after completely disap- 
pearing, it returned with its original brightness. 
When the spot was most luminous, the disc of the 
planet did not appear exactly round, but the bright 
part of the southern limb, that terminated this spot, 
appeared to project like a bright cap, whose exterior 
arch was a portion of a circle of a larger radius 
than the rest of the planet's limb. This appear- 
ance resembled that of the new moon surrounding 
the old, spoken of before, and seems to be an optical 
deception arising from the same cause. 



In 1719, a favorable opportunity occurred for 
observing the spots upon Mars. When within two 
degrees of its perihelion, it was in opposition to the 
sun, and appeared superior to Jupiter in magnitude 
and brightness. Maraldi observed it at that time, 
through a refracting telescope thirty-four feet long, 
and saw the appearance represented in the adjoin- 
ing figures. A long belt, extending half-way round 





its disc, was joined hy a shorter belt, forming with 
it an obtuse angle. By the motion of this angular 
point, Maraldi found its daily period to be twenty- 
four hours and forty minutes — the very same with 
that of Cassini. These luminous spots were ob- 
served, from 1777 to 1783, by Herschel, who, by 
ascertaining the changes in their position, has 
determined the inclination of the axis, and the 
1. 2. 3. 






place of the nodes, of Mars. The polar spots are 
represented in the several figures accompanying, in 



172 



WONDERS OF THE HEAVENS 



which a is the south polar, and b the north polar, 
spot. In the second figure, the south polar spot 
has a singular appearance, similar to what was 
observed by Maraldi. In consequence of its great 
splendor, it seems to project beyond the disc of the 
planet, producing a break at c, increased by the 
gibbous appearance of the planet. The south polar 
spot is represented in the other figures, which com- 
plete the whole equatorial circle of appearances, as 
they were observed in immediate succession. These 
figures are all connected in one projection. The 




centre of the circle marked 17 is placed on the 
circumference of the inner circle, by making its 
distance from the centre of the circle marked 15 
answer to the interval of time between the two 
observations, properly calculated and reduced to 
sidereal measure. The same has been done with 
regard to the circles marked 18, 19, 20, &,c. And 
it will be found, by placing any of these connected 
circles so as to have its contents in a similar situa- 
tion with the figures in the single representation 
which bear the same number, that there is a suffi- 
cient resemblance between them ; but some allow- 
ance must be made for the distortion of this kind of 
projection. 

From the similarity between Mars and the earth, 
in their diurnal motion, and in the position of their 
equators, Dr. Herschel imagined that the bright 
spots at the poles of this planet are produced by 
the reflection of the sun's light from its frozen 
regions, and that the melting of masses of polar ice 
is the cause of the variation in the magnitude of 
the spots. Hence, in 1781, when the antarctic 
glaciers had not felt for twelve months the thawing 



influence of the sun, the south polar spot was 
extremely large, and in 1783 it had suffered a con- 
siderable diminution from an exposure of eight 
months to the solar rays. 

As the diurnal rotation of Mars has been accu- 
rately established by the motion of its spots, it was 
natural to expect that, in conformity to the laws of 
gravity, it should exhibit a spheroidal form. Owing 
to its gibbous appearance, there is difficulty in 
taking accurate measures of its diameters. Dr. 
Herschel finally succeeded in the attempt, and 
found its figure to be an oblate spheriod, whose 
equatorial diameter is to its polar nearly as sixteen 
to fifteen; that the inclination of its axis to the 
ecliptic is fifty-nine degrees forty-two minutes ; 
that the node of the axis is in seventeen degrees 
forty-seven minutes of the Fishes ; that the obliquity 
of its ecliptic is twenty-eight degrees forty-two 
minutes ; and that the time of its ^diurnal rotation 
is twenty-four hours thirty-nine minutes. The 
remarkable flattening at the poles of Mars probably 
arises from a considerable variation in the density 
of its different parts. La Place computed its density 
to be about three fourths of that of the earth. 

From the circumstance of this planet's having no 
satellite, and appearing to require light in the sun's 
absence, it has been imagined that Mars is phos- 
phorescent, and gives out during the night the light 
it has imbibed during the day. 

ULTRA ZODIACAL PLANETS. 

Four very small planets have been discovered 
since the commencement of the nineteenth century, 
lying between the orbits of Mars and Jupiter, and 
have been named respectively Ceres, Pallas, Juno, 
and Vesta. 

These additions do not merely present us with a 
few insulated facts similar to those with which we 
were before acquainted. They exhibit to us new 
and unexpected phenomena, that seem to destroy 
the harmony of the solar system, as far as it de- 
pends on the magnitudes and distances of the 
planets, or on the form and position of their orbits. 

The planets which were before considered as 
composing the system, were placed at somewhat 



WONDERS OF THE HEAVENS 



173 



regular distances from the sun. They moved from 
west to east, and at such intervals as to prevent 
any extraordinary derangements which might arise 
from their mutual action. 

The magnitudes, too, of the four nearest the sun 
increased with their distance from that centre, and 
the eccentricity, as well as the inclination of the 
orbits was comparatively small. In the system as 
now known, however, we find the four small planets 
placed as above stated, all of them at nearly the 
same distance from the sun, and moving in very 
eccentric orbits, which intersect each other, and 
are greatly inclined to the plane of the ecliptic. 
The satellites of the planet Herschel are another 
exception, for they move nearly at right angles to 
the plane of his orbit ; and the direction of their 
motion is opposite to that in which all the other 
planets, whether primary or secondary, circulate 
in their respective orbits. The most remarkable 
peculiarity of these small planets must consist in 
their feeble power of gravitation. A man placed 
on one of them would spring, with ease, sixty feet 
high, and sustain no greater shock in his descent 
than he does on the earth from leaping a yard. On 
such planets, giants might exist; and those enormous 
animals, which on earth require the buoyancy of 
water to sustain them, might there be dwellers 
on the land. 

CERES 

Was discovered at Palermo, Sicily, on the first 
of January, 1801, by Piazzi, an ingenious observer, 
who afterward distinguished himself by his astro- 
nomical labors. This new celestial body was 
then situated in the Bull, and was observed by 
Piazzi till the twelfth of February, when a danger- 
ous illness compelled him to discontinue his obser- 
vations. It was, however, again discovered by 
Olbers, at Bremen, on the first of January, 1807, 
nearly in the place where it was expected from 
calculation. The nebula with which it was sur- 
rounded gave it the appearance of a comet. 

Ceres is of a ruddy color, and appears about the 
size of a star of the eighth magnitude. It seems to 
be surrounded with a large, dense' atmosphere, and 



plainly exhibits a disc when examined with a 
magnifying power of two hundred. This planet 
performs its revolution round the sun in four years 
seven months and ten days; and its mean distance 
from that luminary is nearly two hundred and 
sixty-three millions of miles. The eccentricity of its 
orbit is a little greater than that of Mercury, while 
its inclination to the ecliptic exceeds that of all the 
old planets. The observations which have been 
made upon this celestial body do not seem suffi- 
ciently correct to enable us to determine its magni- 
tude with any degree of accuracy. According to 
the measurements of Herschel, the diameter of 
Ceres does not exceed one hundred and sixty-three 
miles, while the observations of Schroeter make is 
about sixteen hundred miles. 

PALLAS 

Was discovered at Bremen, on the twenty- 
eighth of March, 1802, by Olbers, the same 
astronomer who rediscovered Ceres. It is nearly 
of the same apparent magnitude with Ceres, but of 
a less ruddy color. It is surrounded with a nebu- 
losity of almost the same extent, and performs its 
annual revolution in nearly the same period. 

The planet Pallas, however, is distinguished in 
a remarkable manner from Ceres, and all the other 
primary planets, by the great inclination of its 
orbit. While these bodies are revolving round the 
sun in almost circular paths, rising only a few 
degrees above the plane of the ecliptic, Pallas 
ascends above this plane at an angle of about 
thirty-five degrees, which is nearly five times 
greater than the inclination of Mercury. From 
the eccentricity of Pallas being greater than that of 
Ceres, or from a difference of position in the line of 
their apsides, while their mean distances are nearly 
equal, the orbits of these two planets mutually 
intersect, a phenomenon altogether anomalous in 
the solar system. 

The diameter of Pallas has not been determined 
with accuracy. Herschel made it only eighty miles, 
while Schroeter made it between two and three 
thousand miles, which is much larger than the 
magnitude he assigned to Ceres. Its mean distance 



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174 



WONDERS OF THE HEAVENS 



from the sun is over two hundred and sixty-three 
millions of miles. ^ 

JUNO 

Was discovered by Harding, on the first of Sep- 
tember, 1804. While this astronomer was forming 
an atlas of all the stars which are near the orbits 
of Ceres and Pallas, he observed, in the constella- 
tion of the Fishes, a small star, (as he thought,) of the 
eighth magnitude, which was not mentioned in the 
catalogue by La Lande ; and, being ignorant of its 
longitude and latitude, he put it down in his chart 
as nearly as he could estimate with the eye. Two 
days after the star had disappeared ; but he per- 
ceived another, which he had not seen before, 
resembling the first in size and color, and situated 
a little to the south-west of its place. He observed 
it again on the fifth of September, and, finding that 
it had moved a little farther to the south-west, he 
concluded that it belonged to the planetary system. 
The planet Juno is of a reddish color, and is free 
from that nebulosity which surrounds Pallas. Its 
diameter is less, and its distance greater, than those 
of the other new planets. It is distinguished from 
all the other planets by the great eccentricity of its 
orbit; and the effect of this is so very sensible, that 
it passes through the half of its orbit which is 
bisected by its perihelion in half the time that it 
employs in describing the other part, which is 
farther from the sun. From the same cause, its 
greatest distance from the sun is double the least 
distance, the difference between the two distances 
being about one hundred and twenty-seven millions 
of miles. Its mean distance from the sun is two 
hundred and fifty-three millions of miles. 

VESTA. 

From the regularity observed in the distances 
from the sun of the planets formerly known, some 
astronomers supposed that a planet existed between 
the orbits of Mars and Jupiter. The discovery of 
Ceres confirmed this happy conjecture ; but the 
opinion which it seemed to establish respecting the 
harmony of the solar system, appeared to be com- 
pletely overturned by the discovery of Pallas and 



Juno. Olbers, however, imagined that these small 
celestial bodies were merely the fragments of a 
larger planet, that had been burst asunder by 
some internal convulsion, and that several more 
might yet be discovered between the orbits of Mars 
and Jupiter. He therefore concluded, that, though 
the orbits of all these fragments might be differently 
inclined to the ecliptic, yet, as they all must have 
diverged from the same point, they ought to have 
two common points of reunion, or two nodes in 
opposite regions of the heavens, through which all 
the planetary fragments must pass sooner or later. 
One of these nodes Olbers found to be in the Virgin, 
the other in the Whale ; and it was actually in the 
latter region that Harding discovered the planet 
Juno. With the intention, therefore, of detecting 
other fragments of the supposed planet, Olbers 
examined, three times a year, all the little stars in 
the opposite constellations of the Virgin and the 
Whale, till his labors were crowned with success, 
on the twenty-ninth of March, 1807, by the dis- 
covery of a new planet, to which he gave the name 
Vesta. 

As soon as this discovery was made known in 
England, the planet was observed by Groombridge, 
who continued his observations, from the twenty- 
sixth of April to the twentieth of May, 1807, with 
an astronomical circle, when, from its having ceased 
to be visible on the meridian, he had recourse to 
equatorial instruments. On the eleventh of Au- 
gust, the meridional observations were renewed, 
from vfhich Groombridge computed part of the ele- 
ments of its orbit, and had the good fortune to 
observe the ecliptic opposition of the planet. 

Vesta is of the fifth or sixth magnitude, and may 
be seen in a clear evening with the naked eye. Its 
light is more intense, pure, and white, than any of 
the other three. It is not surrounded with any 
nebulosity, and has no visible disc. The orbit of 
Vesta cuts the orbit of Pallas, but not in the same 
place where it is cut by that of Ceres. According 
to the observations of Schroeter, the apparent 
diameter of Vesta is only 0-488 of a second, or one 
half of what he found to be the apparent diameter 
of the fourth satellite of Saturn; and yet it is 



WONDERS OF THE HEAVENS. 



175 



remarkable that its light is so intense that Schroeter 
saw it several times without the aid of an instru- 
ment. Vesta is two hundred and twenty-five 
millions of miles from the sun. 

It has been supposed that this planet had been 
previously observed, and mistaken for a fixed star, 
since a small star, situated in the same place and 
observed by Monnier, has since disappeared. 

The orbits of these four small planets, projected 
from the places of their perihelia, are represented 




in the figure. These orbits appear to intersect 
each other in various places, and it is obvious that 
the points of intersection must be perpetually shift- 
ing, according to the changes in the aphelia of 
the planets. 



SECTION III. 



Jupiter's form — Its situation — Length of its year^Rapidity of rota- 
tion — Small change in its seasons — Alternately morning and eve- 
ning star — Its belts — Degree of oblateness — Cause of the belts — 
Jupiter's satellites — Particulars respecting them — Velocity of light 
— Saturn's size compared with the earth's — Surrounded by a ring 
— Singular form of Saturn — Its spots and belts — Why this planet 



is more oblate than Jupiter — Saturn's satellites — Position of their 
orbits — Theories concerning the rings — Their different appear- 
ances — Their revolution — How they are sustained — Herschel, par- 
ticulars of— Its satellites — Their peculiarities — How kept in their 
orbits. 

JUPITER. 
The planet Jupiter revolves about its axis in ten 
hours nearly. Its form, like that of Mars and of 
the earth, is an oblate spheroid, the equatorial being 
to the polar diameter as fourteen to thirteen; so 
that its poles are three thousand miles nearer its 
centre than its equator is. This results from its 
quick motion round its axis ; for the fluids, together 
with the light particles which they can carry or 
wash away with them, recede from the poles, which 
are at rest, towards the equator, where the motion 
is quickest, until there be a sufficient number accu- 
mulated to make up the deficiency of gravity lost 
by the centrifugal force which always arises from 
a quick motion round an axis : and when the defi- 
ciency of weight or gravity of the particles is made 
up by a sufficient accumulation, there is an equili- 
hrium, and the equatorial parts rise no higher. 
The ratio (fourteen to thirteen) was obtained from 
observations by Herschel, and it is a remarkable 
coincidence between theory and observation, that, 
from the influence of the equatorial parts of the 
planet upon the motion of the nodes of the satellites, 
La Place found the proportion very nearly the 
same. 




Jupiter, the largest of all the planets, is still 
higher in the system than Pallas, being about four 



176 



WONDERS OF THE HEAVENS 



hundred and ninety millions of miles from the sun, 
and, going at the rate of twenty-nine thousand 
miles an hour in its orbit, completes its revolution 
in a little less than twelve years of our time. This 
planet is thirteen hundred times larger than the earth, 
its diameter being nearly eighty-six thousand miles, 
which is nearly eleven times the diameter of the 
earth. In the figure, Jupiter's surface is compared 
to that of all the other planets taken together. 

Jupiter's year contains more than ten thousand 
days, and the diurnal velocity of the parts near its 
equator is nearly as great as the swiftness with 
which the planet moves in its annual orbit. By 
this rapid rotation, the equatorial inhabitants are 
carried twenty-eight thousand miles an hour, beside 
the twenty-nine thousand above mentioned, which 
is common to all parts of its surface by the annual 
motion. 

Jupiter is the brightest of all the planets, except 
Venus. It shines with a bright white light, and 
does not vary in apparent size and brightness so 
much as Mars. It is the largest planet in the solar 
system. A body weighing one pound at the earth, 
if removed to the surface of Jupiter would weigh 
two and a half pounds nearly. 

The axis of Jupiter is so nearly perpendicular to 
its orbit that it has no sensible change of seasons, 
which is a great advantage, and wisely ordered by 
the Author of nature ; for, if the axis of this 
planet were inclined any considerable number of 
degrees, just so many degrees round each pole 
would in their turn be almost six of our years 
together in darkness; so that vast tracts of land 
would be rendered uninhabitable by any considera- 
ble inclination of its axis. 

When Jupiter is in conjunction, it rises, sets, 
and comes to the meridian, with the sun, but is 
never observed to transit the sun's disc ; when in 
opposition, it rises at sunset, sets at sunrise, and 
comes to the meridian at midnight. This is a 
sufficient proof that Jupiter revolves round the sun 
in an orbit including that of the earth. 

When viewed in opposition, Jupiter appears 
larger and more luminous than at other times, 
being then much nearer the earth than a little 



before or after conjunction. When its longitude is 
less than that of the sun, it will appear in the east 
before the sun rises, and will then be a morning 
star. When its longitude is greater than that of 
the sun, it will appear in the west after sunset, and 
will then be an evening star. 

When Jupiter is observed with good telescopes, 
several belts or bands are perceived extending 
across its disc in lines parallel to its equator. 
These belts are by no means alike at all times, 
either in number, distance, or position. They 
have even been seen broken up and distributed 
over the whole face of the planet ; but this phenom- 
enon is very rare. Branches running out from 
them, and subdivisions, as well as dark spots like 
strings of clouds, are not uncommon, and from 
these attentively watched it has been concluded 
that this planet revolves on an axis perpendicular 
to the direction of the belts. It is very remark- 
able, and forms a satisfactory comment on the 
reasoning by which the spheroidal figure of the 
earth was deduced from its diurnal rotation, that 
the outline of Jupiter's disc is not circular, but 
elliptic, being much flattened in the direction of its 
axis of rotation. This appearance is no illusion, 
1 9. 







but is confirmed by measures with the micrometer, 
which assign one hundred and seven to one hun- 
dred as the proportion of the equatorial to the 



WONDERS OF THE HEAVENS 



177 



polar diameters.* And, to confirm in the strongest 
manner the truth of those principles on which former 
conclusions were founded, and fully to authorize 
their extension to this remote planet, it appears, 
on calculation, that this is really the degree of 
oblateness, which corresponds, on those principles, 
to the dimensions of Jupiter, and to the time of its 
rotation. 

Herschel perceived the whole disc of Jupiter 
covered with small curved belts, or rather lines, 
that were not continuous across the disc. This 
appearance is represented in figures 1 and 2. The 
parallel belts are most common, and, in clear 
weather, may be seen with a magnifying power 
of forty. The appearance they presented when 
viewed through Herschel's instruments, is shown 
in figures 3 and 4. Sometimes they are inter- 
rupted in their length, as in figure 3 ; at others they 
seem to increase and diminish alternately, to run 
into one another, or to separate into others of a 
smaller size. Bright and dark spots are frequently 
visible, as in figure 4. Some of these revolve with 
greater rapidity than others, from which it appears 
that they are not permanent spots upon the planet 
itself. 

When Jupiter was in perihelion, in 1785 and 
1786, Schroeter observed the belts with a tele- 
scope magnifying one hundred and fifty times. He 
perceived upon the disc several new spots, which 
were black and round. In 1787, he saw two dark 
belts in the middle of the disc, and near them 
two white and luminous belts, resembling those 
observed by Campani. The equatorial zone, which 
was comprehended between the two dark belts, 
had assumed a dark gray color, bordering upon 
yellow. The northern dark belt then received a 
sudden increase of size, while the southern became 
partly effaced, and afterwards increased into an 
uninterrupted belt. The luminous belts also suffer- 
ed several changes, growing sometimes narrower, 
and sometimes one half larger, than their original 
size. 

Different opinions have been entertained respect- 

* The younger Herschel. This ratio differs but little from that 
before given. 

23 



ing the cause of these belts and spots. By some 
they have been regarded as clouds, or as openings 
in the atmosphere of the planet. Others regard 
these appearances as indications of great physical 
revolutions, which are perpetually agitating and 
changing the surface of the planet. The first of 
the above opinions sufficiently explains the varia- 
tions in the form and magnitude of the belts, but 
does not account for the permanence of some of the 
spots, and for the parallelism of the belts. 

The spot first observed by Cassini, which reap- 
peared eight times between the years 1665 and 
1708, could not possibly have been occasioned by any 
atmospherical variations ; and its disappearance for 
five years is a presumptive, though not a decisive, 
argument that it arose from some changes in the 
body of the planet. Brewster, however, was dis- 
posed to think, from the frequent appearance of this 
spot, that it was permanent on the body of Jupiter, 
and that its disappearance was owing to the inter- 
position of clouds in the atmosphere of the planet. 
If it were the effect of an earthquake or inundation, 
or if it were the mark of a new island or continent, as 
some have conjectured, how should we account for 
its reappearance after five years in the same form 
and position ? May we not suppose that the clouds 
of Jupiter, partaking of the great velocity of its 
diurnal motion, are formed into strata parallel 
with the equator, that the body of Jupiter reflects 
less light than the clouds, and that the belts are 
the body of the planet seen through the parallel 
interstices which lie between the different strata of 
clouds? The spot seen by Cassini will, of course, 
only be seen when it is immediately below one of 
these interstices, and will therefore always appear 
as if it accompanied one of the belts. 

Herschel the younger has the following on this 
subject. The parallelism of the belts to the 
equator of the planet, their occasional variations, 
and the appearances of spots seen upon them, 
render it extremely probable that they subsist in 
the atmosphere of the planet, forming tracts of con- 
paratively clear sky, determined by currents analo- 
gous to our trade winds, but of a much more steady 
and decided character, as might indeed be expected 



178 



WONDERS OF THE HEAVENS. 



from the immense velocity of its rotation. That it 
is the comparatively darker body of the planet 
vv^hich appears in the belts, is evident from this, 
that they do not come up in all their strength to 
the edge of the disc, but fade av^^ay gradually before 
they reach it. 

By directing a telescope to Jupiter, it is found 
to be attended hy four small stars, ranged nearly in 
a right line parallel to the plane of its belts. 
These stars are the moons of Jupiter, which move 
round their primary in different periods, and at 
unequal distances. The third and fourth have 
been sometimes seen with the naked eye ; but only 
when the air is uncommonly pure can we expect to 
be gratified with so rare a sight. 

The discovery of these satellites was made by 
Galileo, in 1610; and this maybe considered as 
one of the first fruits of the invention of the tele- 
scope. They are distinctly visible with a telescope 
of a moderate power. Their relative situation 
with regard to Jupiter, as well as to each other, is 
constantly changing. Sometimes they may be all 
seen on one side of Jupiter, and sometimes all on 
the other. They are designated by their distances 
from Jupiter, that being called the first whose 
distance from Jupiter is the least when at the 
greatest elongation, and so on with the others. 
They are of very different magnitudes, some of 
them being greater than our earth, while others 
are not so large as the moon. Their apparent 
diameters being insensible, their real magnitudes 
cannot be exactly measured. The attempt has 
been made, by observing the time they enter the 
shadow of Jupiter ; but there is a great discordance 
in the observations which have been made to obtain 
this circumstance, and, of course, the result of 
these observations must be very discordant. The 
third, however, is the greatest; the fourth is the 
second in magnitude ; the first the third in magni- 
tude ; and the second is the least. 

These satellites were observed with great assi- 
duity during the last century, and the tables of 
their motions have been brought to a degree of 
perfection which the most sanguine expectations 
could not have anticipated. To geographers and 



astronomers the system of Jupiter and its moons is 
equally interesting. Though but a short time com- 
paratively has elapsed since their discovery, yet, 
from the extreme shortness of their revolutions, 
they present in a short period those great and 
interesting changes which are not effected in the 
course of many centuries in the planetary system. 

The moon nearest Jupiter revolves in its orbit in 
forty-two and a half hours : the most remote in about 
seventeen days of our time. The satellites of 
Jupiter revolve from west to east, (following the 
analogy of the primaries, and of our moon,) in 
planes nearly coincident with that of the planet's 
equator. This latter plane is inclined about three 
degrees to the orbit of the planet, and is therefore 
but little different from the plane of the ecliptic. 
Accordingly, we see their orbits projected very 
nearly into straight lines, in which they appear to 
oscillate to and fro, sometimes passing before the 
planet and casting shadows on its disc, (which 
shadows are very visible in good telescopes, like 
small, round ink spots,) and sometimes disappear- 
ing behind the body, or being eclipsed in its shadow 
at a distance from it. 

The four moons must afford many curious phe- 
nomena to the inhabitants of the primary, in their 
nightly course through the heavens. The first 
moon, or that nearest the planet, is two hundred 
and thirty thousand miles from its centre, and will 
appear from its surface four times larger than our 
moon does to us ; the second, being further distant, 
will appear about the size of our moon ; the third, 
somewhat less; and the fourth, which is distant a 
million of miles, will appear about one third the 
size of our moon. 

The planet, if seen from its nearest moon, will 
present a surface a thousand times as large as our 
moon does to us, and will appear in the form of a 
crescent, a half-moon, a gibbous phase, and a full 
moon, in regular succession, every forty-two and a 
half hours. 

When the satellites are on the right hand, or 
west of Jupiter, approaching it, or east of Jupiter, 
receding from it, they are then in the superior 
parts of their orbits or furthest from the earth. On 



WONDERS OF THE HEAVENS 



179 



the contrary, when the satellites are on the right 
hand, or west of Jupiter, receding from it, or east 
of Jupiter, approaching it, they are then in the 
inferior part of their orbits, or nearest the earth. 

An extremely singular relation subsists between 
the mean angular velocities, or mean motions, (as they 
are termed,) of the three first satellites of Jupiter. 
If the mean angular velocity of the first satellite be 
added to twice that of the third, the sum will equal 
three times that of the second. From this relation 
it follows, that, if from the mean longitude of the 
first added to twice that of the third be subtracted 
three times that of the second, the remainder will 
always be the same, or constant, and observation 
informs us that this constant is one hundred and 
eighty degrees, or two right angles ; so that, the 
situations of any two of them being given, that of 
the third may be found. It has been attempted to 
account for this remarkable fact on the theory of 
gravity by their mutual action. One curious con- 
sequence is, that these three satellites cannot be all 
eclipsed at once; for, in consequence of the last- 
mentioned relation, when the second and third lie 
in the same direction from the centre, the first must 
lie on the opposite, and, therefore, when the first is 
eclipsed, the other two must lie between the sun 
and planet, throwing its shadow on the disc, and vice 
versa. One instance only is on record when Jupiter 
has been seen without satellites, viz. by Molyneux, 
November, 1681. 

The discovery of Jupiter's satellites by Galileo, 
forms one of the most memorable epochs in the 
history of astronomy. The first astronomical solu- 
tion of the great problem of ''the longitude" (the 
most important for the interests of mankind which 
has ever been brought under the dominion of strict 
scientific principles) dates immediately from their 
discovery. The final and conclusive establishment 
of the Copernican system of astronomy may also be 
considered as referable to the discovery and study 
of this exquisite miniature system, in which the 
laws of the planetary motions, as ascertained by 
Kepler, and especially that which connects their 
periods and distances, were speedily traced, and 
found to be satisfactorily maintained. And (as if 



to accumulate historical interest on this point) it is 
to the observation of their eclipses that we owe the 
grand discovery of the aberration of light, and the 
consequent determination of the enormous velocity 
of that wonderful element. This we must explain. 
The earth's orbit being concentric with that of 
Jupiter, and interior to it, their mutual distance is 
continually varying, the variation extending from 
the sum to the difference of the radii of the two 
orbits, and the difference of the greater and least 
distances being equal to a diameter of the earth's 
orbit. Now, it was observed by Roemer, on com- 
paring together observations of eclipses of the 
satellites during many successive years, that the 
eclipses at and about the opposition of Jupiter (or 
its nearest point to the earth) took place too soon — 
sooner, that is, than, by calculation from an average, 
he expected them ; whereas those which happened 
when the earth was in the part of its orbit most 
remote from Jupiter were always too late. Con- 
necting the observed error in their computed times 
with the variation of distance, he concluded, that, 
to make the calculation on an average period 
correspond with fact, an allowance in respect of 
time behooved to be made proportional to the 
excess or defect of Jupiter's distance from the earth 
above or below its average amount, and such that 
a difference of distance of one diameter of the 
earth's orbit should correspond to 16 m. 26 s. 6 
of time allowed. Speculating on the probable 
physical cause, he was naturally led to think of 
the gradual, instead of the instantaneous, propaga- 
tion of light. This explained every particular of 
the observed phenomenon; but the velocity re- 
quired {one hundred and ninety two thousand miles 
per second) was so great as to startle many, 
and, at all events, to require confirmation. This 
has been afforded since, and of the most unequivo- 
cal kind, by Bradley's discovery of the aberration 
of light. The velocity of light deduced from this 
last phenomenon differs by less than one eightieth 
of its amount from that calculated from the eclipses, 
and even this difference will no doubt be destroyed 
by nicer and more rigorously reduced observa- 
tions. 



PKHMSr—flffW)'"''"'''^"^ 



H^SBg 



180 



WONDERS OF THE HEAVENS 



Tne orbits of Jupiter's satellites are but little 
eccentric. Those of the two interior, indeed, have 
no perceptible eccentricity: Their mutual action 
produces in them perturbations analogous to those 
of the planets about the sun, and which have been 
diligently investigated by Laplace and others. By 
assiduous observation it has been ascertained that 
they are subject to marked fluctuations in respect 
of brightness, and that these fluctuations happen 
periodically, according to their position with respect 
to the sun. From this it has been concluded, 
apparently with reason, that they turn on their 
axes, like our moon, in periods equal to their 
respective sidereal revolutions about their primary. 

SATURN. 

This planet is about nine hundred millions of 
miles from the sun, and, travelling at the rate of 
twenty-two thousand miles an hour, performs its 
annual circuit in twenty-nine and a half of our 
years, which make only one of its years. The 
planet's diameter is seventy-nine thousand miles, 
and, therefore, it is nearly ten hundred times larger 
than our globe. It is surrounded by a broad thin 
ring, as an artificial globe is by a horizon. But of 
this hereafter. 

Saturn shines with a very feeble light compared 
with that of Jupiter, partly on account of its greater 
distance, and partly from its dull red color. In 
size, it is the next planet to Jupiter in the solar 
system. A body weighing a pound at the earth's 
surface, would weigh a little more than one pound 
and one third at the surface of Saturn. The appa- 
rent motion of Saturn in its orbit is subject to 
irregularities similar to those of Jupiter and Mars. 
It commences and finishes its retrograde motion 
when the planet is about one hundred and nine 
degrees from the sun, before and after opposition. 
The arc in which it retrogrades is about six and 
one third degrees, and the time of its retrograde 
motion is nearly one hundred and thirty-one days. 

When we look at the body of Saturn with a good 
telescope, it appears, like most of the other planets, 
to be of a spheroidal form, arising from a rapid 
rotation round its axis. Herschel measured the 



diameters, and at first found that the equatorial 
was to the polar as eleven to ten nearly. How- 
ever, he afterwards corrected this result by new 
observations, and found the proportion to be more 
nearly as twelve to eleven. Until the year 1805, 
Herschel regarded Saturn as an accurate spheroid ; 
but on the 12th of April, of that year, he was struck 
with a very singular appearance presented by the 
planet. The flattening at the poles did not seem 
to begin till a very high latitude ; so that the real 
figure of the planet resembled a square, or rather 
a parallelogram, with the four corners rounded ofl" 
deeply, but not enough to make a spheroid. After 
examining Saturn with his telescopes, and compar- 
ing it with the form of Jupiter, Herschel concluded 
that this was the real form of the planet. He also 
found that the latitude of the longest diameter was 
about forty-three and a half degrees. 

The surface of Saturn is diversified, like that of 
some of the other planets, with dark spots and 
belts. Huygens observed five belts, which were 
nearly parallel to the equator. Herschel also 
observed several belts, which were, in general, 
parallel with the ring. On the 11th of November, 
1793, immediately south of the shadow of the ring 
upon the planet, he perceived a bright, uniform, 
and broad belt, and close to it a broad and darker 
belt, divided by two narrow white streaks; so that 
he saw five belts, three of which were dark, and 
two white. The dark belts had a yellowish tinge. 
These belts generally cover a larger zone of the 
disc of Saturn, than the belts of Jupiter occupy on 
the surface of that planet. 

Herschel also perceived dark spots on Saturn's 
disc, and, by the changes in their position, deter- 
mined the diurnal rotation of the planet to be per- 
formed in about ten hours and a quarter, round an 
axis perpendicular to the plane of the rings. 

It has been made known already that the flatten- 
ing at the poles of the planets arises from the cen- 
trifugal force of their equatorial parts. On account 
of the great diameter of Jupiter, and the rapidity of 
its daily motion, its equatorial parts move with im- 
mense velocity, and, in consequence of their great 
centrifugal force, this planet is more flattened at 



lU BUMBSI I 



I f '.wm ' PL i*'"""^ ' ^— * i *' i j i wi I * ' 



WONDERS OF THE HEAVENS. 



181 



its poles than either the earth or Mars. It is re- 
markable, however, that Saturn should be more 
flattened at its poles than Jupiter, though the 
velocity of the equatorial parts of the former is 
much less than that of the latter. When we con- 
sider, however, that the ring of Saturn lies in the 
plane of its equator, and that its density is equal 
to, if not greater, than that of the planet, we shall 
find no difficulty in accounting for the great accu- 
mulation of matter at the equator of Saturn. The 
ring acts more powerfully upon the equatorial 
regions of Saturn, than upon any other part of its 
disc, and, by diminishing the gravity of these parts, 
it aids the centrifugal force in flattening the poles of 
the planet. Had Saturn never revolved on its axis, 
the action of the ring would of itself have been 
sufficient to give it the form of an oblate spheroid. 

Satellites of Saturn. — The planet Saturn is sur- 
rounded with no fewer than seven satellites, which 
supply it with light during the absence of the sun. 
The importance of these moons will be at once 
perceived, when it is stated that the sun appears at 
Saturn only one ninetieth as large as to us. 

The fourth of the satellites was discovered by 
Huygens, on the 25th of March, 1655. Cassini 
discovered the fifth, in October, 1671 ; the third on 
the 23d of December, 1672. The sixth and 
seventh, were discovered by Herschel, in 1789, 
and are nearer to Saturn than the rest, though, to 
avoid confusion, they are named in the order of 
their discovery. 

These satellites are all so small, and situated at 
such distances from the earth, that they cannot 
be seen except with powerful telecopes. War- 
gentin saw the five old satellites with an achromatic 
telescope of ten feet, and Herschel saw them 
distinctly with a power of sixty applied to his ten- 
feet reflector. The sixth and seventh are the 
smallest of the whole; the first and second are 
the next smallest; the third is greater than the 
first and second; and the fourth is the largest of 
them all. The fifth surpasses all of them, except 
the fourth, in brightness, when it is at its western 
elongation from Saturn, but at other times it is very 
small, and entirely disappears at its eastern elon- 



gation. This phenomenon, which was at first 
observed by Cassini, appears to arise from one part 
of the satellite being less luminous than the re§.t. 
In consequence of the satellite's rotation on its axis, 
this obscure part of the disc, is turned toward the 
earth when it is in the part of its orbit east of 
Saturn ; and the luminous part of its surface be- 
comes visible while it is in the western part of its 
orbit. Herschel observed this satellite through all 
the variations of its light ; and concluded, that, like 
our moon, and the satellites of Jupiter, it turned 
round its axis in the same time that it performed its 
revolution round the primary. When he used his 
twenty-feet telescope, he never lost sight of the 
satellite, even when its light was most faint. 

The theory of the satellites of Saturn is less 
perfect than that of the satellites of Jupiter. The 
difficulty of observing their eclipses, and of mea- 
suring their elongations from Saturn, have prevent- 
ed astronomers from determining, with their usual 
precision, the mean distances and the revolutions of 
these secondaries. 

In the position of their orbits there is something 
quite remarkable: while the orbits of the six inner 
satellites all lie nearly in the plane of the ring, the 
orbit of the fifth (most distant) moon deviates con- 
siderably from this plane. The fourth moon is 
probably not much inferior to Mars in size. The 
fifth is the only one whose theory has been examin- 
ed further than suffices to verify Kepler's laws of 
the periodic times, which, under certain reserva- 
tions, holds good of this, as of the system of Jupiter. 
It exhibits, as has been stated, periodic defalcations 
of light, which prove its revolution on its axis in 
the time of its sidereal revolution about Saturn. 
The next in order (proceeding inwards) is tolerably 
conspicuous ; the three next very minute, and re- 
quiring pretty powerful telescopes to see them; 
while the two interior satellites, which just skirt 
the edge of the ring, and move exactly in its plane, 
have never been discerned but with the most pow- 
erful telescopes which human art has yet construct- 
ed, and then only under peculiar circumstances. 
At the time of the disappearance of the ring (to 
ordinary telescope's) they have been seen threading 



182 



WONDERS OF THE HEAVENS 



like beads the almost infinitely thin fibre of light 
to which it is then reduced, and for a short time 
advancing off it at either end, speedily to return, 
and hastening to their habitual concealment. 
Owing to the obliquit}^ of the ring, and of the orbits 
of the satellites, to Saturn's ecliptic, there are no 
eclipses of the satellites (the interior ones except- 
ed) until near the time when the ring is seen 
edgewise. 

The inequalities in the surface of the ring are 
considered by La Place as absolutely necessary 
for maintaining it in equilibrium around Saturn ; 
and he has shown, that, if the ring were a regular 
body, similar in all its parts, its equilibrium would 
be disturbed by the slightest force, such as the 
attraction of a comet or a satellite, and that it 
would finally be precipitated upon the surface of 
the planet. Hence, that philosopher concluded 
that the different rings with which Saturn is encir- 
cled are irregular solids, of unequal breadth in 
different parts of their circumference, so that their 
centres of gravity do not coincide with their centres 
of figure ; and that these centres of gravity may be 
considered as so many satellites circulating round 
Saturn, at distances dependent on the inequality of 
the parts of each ring, and with periods of rotation 
equal to those of their respective rings. Hence, 
the ring will turn round its centre of gravity in the 
same time that it revolves round Saturn. It is 
obvious that the action of the sun and the satellites 
of Saturn upon these rings, ought to produce mo- 
tions of precession analogous to those of the earth's 
equator; and that, as these motions ought to be 
different for each ring, they ought finally to move 
in different planes. This result is, however, con- 
trary to observation ; and La Place discovered that 
the action of the equator is the cause that retains 
all the rings in one plane. 

Not content with explaining the various phe- 
nomena presented by the rings, astronomers have 
attempted also to account for their formation. 
Maupertuis maintained that this luminous girdle 
was the tail of a comet, which the attraction of 
Saturn had compelled into its service. Mairan 
asserted that the diameter of the planet was origin- 



ally equal to that of its outer ring, and that by 
some cause the external shell of Saturn was broken 
in pieces, which were attracted by its body ; but 
that the equatorial parts of the shell remained 
entire, and thus formed a ring about the planet. 
Buffon imagined that the ring is a part of the 
equator, which has been detached by the centrifu- 
gal force. It may be sufficient to observe that we 
might as well attempt to account for the formation 
of the satellites as the ring; that none of them 
seem to have been the effect of any accidental 
cause ; and that the most rational solution of the 
difficulty is, to suppose that when Saturn was 
created and launched into the heavens, it was at 
the same instant encircled with a luminous ring, to 
answer some important purpose. 

The edge of the ring reflects but little of the 
sun's light to us : the planes of the ring reflect the 
light of the sun, in the same manner as the planet 
does. If we suppose the diameter of Saturn to be 
divided into three equal parts, the diameter of the 
ring is equal to about seven of these parts. The 
ring is detached from the body of the planet in such 
a manner that the distance from its innermost edge, 
to the body of the primary, is equal to the breadth 
of the ring. Stars have been seen through the 
intervening space, though rarely, as the opening, 
in reality of large dimensions, appears quite small 
to us by reason of the distance. 

Galileo was the first who discovered any thing 
uncommon in Saturn. Through his telescope he 
thought that the planet appeared like a large globe, 
with a smaller one on each side of it. In the year 
1610, he gave out his discovery in a Latin sentence, 
the meaning of which was, that he had seen Saturn 
with three bodies ; but the letters of the sentence 
were transposed, to keep his discovery secret for 
a time, lest some other person should pretend to 
the same. After viewing the planet in this form 
for two years, he was surprised to see it become 
quite round, without its adjacent globes, for some 
time. But afterwards he again discovered the 
globes on each side, which, in process of time, 
appeared to change their form ; sometimes appear- 
ing round, sometimes oblong like an acorn, some- 



WONDERS OF THE HEAVENS 



183 



times semicircular, then with horns towards the 
globe in the middle, and growing, by degrees, so 
long and wide as to encompass it, as it were, with 
an oval ring. 

And now Saturn was observed by several others, 
some of whom, either from want of skill in drawing 
what they saw, or of good telescopes to make 
observations with, published figures not very like 
to what it appears through powerful glasses. 

About forty years after this, Huygens, having 
greatly improved the art of grinding object glasses, 
first with a telescope of twelve, and afterward with 
one of twenty-three feet, that magnified a hundred 
times, (Galileo's magnified but thirty times,) dis- 
covered the true shape of Saturn's ring. 

If we bad a view of Saturn and its ring, with 
our eye perpendicular to one of the planes of the 
ring, we should see them as in the figure. But 




our eyes are never elevated so much above either 
plane as to have the visual ray stand at right 
angles to it : our eye, indeed, is never elevated 
more than thirty degrees above the plane of the 
ring. For the most part we view the ring at an 
oblique angle, so that it appears of an oval form, 
more or less oblong according to the different 
degrees of obliquity with which it is viewed. 

When the ring appears as an ellipse, the parts 
about the extremities of the longer axis, reaching 
beyond the disc of the planet, are called " handles," 
(ansae.) They are unequal in size a little before 
and after the ring disappears. The larger handle 
is longer visible before the planet's round phase, 
and appears sooner again after it. As the ellipse 



of the ring grows narrower, the handles appear 
shorter; their extremities disappear first, either 
because of their narrowness, or because the outward 
parts of the rings are less bright than the inward. 

The appearances above described constantly suc- 
ceeding each other in a regular manner, we must 
conclude, then, that the cause producing them is 
constant ; and they are ascribed to a solid body sur- 
rounding the planet, appearing and disappearing 
in succession. As it would not be natural to con- 
clude that this body acquires and loses by turns 
the power of reflecting light, we must suppose that 
it is opaque, and that the variations in its appear- 
ance result from its position and form. 

Thus, it will be bright when it turns toward us 
that face which is illuminated by the sun, and cease 
to be visible when it turns the opposite face. We 
must also lose sight of it when we are so situated 
that its plane passes through the earth's centre; 
for then it can reflect no light to us. Again, we 
cannot see it when its plane passes through the 
sun ; for then only its edge is illuminated, and, as 
it is very thin, it cannot reflect light enough to 
render it visible to us. Yet, if very powerful tele- 
scopes be used, the edge can be seen, and it 
appears like a luminous line on the disc of the 
planet. 

These phenomena afford strong confirmation to 
the hypothesis of an annular surface surrounding 
Saturn. 

It can be demonstrated that the ring, like the 




planet, is an opaque body ; for when the illuminated 
surface of the ring is inclined to the earth, as in 



184 



WONDERS OF THE HEAVENS. 



the figure, it projects a perceptible shadow on the 
globe of Saturn. This figure represents the planet 
surrounded by its rings, and having its body striped 
with dark belts, somewhat similar, but broader and 
less strongly marked, than those of Jupiter, but 
owing doubtless to a similar cause. That the ring 
is a solid opaque substance, is shown by its shadow 
on the planet on the side nearest the sun, and by 
its receiving that of the planet on the other side, as 
shown in the figure. From the belts being parallel 
with the plane of the ring, it may be conjectured 
that the axis of rotation of the planet is perpendicu- 
lar to that plane ; and this conjecture is confirmed 
by the occasional appearance of extensive dusky 
spots on its surface, which, when watched, like the 
spots of Mars and Jupiter, indicate a rotation in 
ten and a half hours about an axis so situated. 
The dimensions of Saturn's rings are as follows: — 

Miles. 

Exterior diameter of exterior ring =176,418 

Interior ditto = 155,27£i 

Exterior diameter of interior ring = 151,690 

Interior ditto =117,339 

Equatorial diameter of tlie body =79,160 

Interval between the planet and interior ring = 19,090 

Interval of the rings , =1,791 

Thickness of the rings not exceeding = 1,000 

The axis of rotation, like that of the earth, pre- 
serves its parallelism to itself during the motion of 
the planet in its orbit; and the same is also the 
case with the ring, whose plane is constantly 
inclined at the same, or very nearly the same, 
angle to that of the orbit, and, therefore, to the 
ecliptic, viz, twenty-eight degrees and forty min- 
utes, and intersects the latter plane in a line 
which makes an angle with the line of equinoxes of 
one hundred and seventy degrees; so that the 
nodes of the ring lie in one hundred and seventy 
degrees and three hundred and fifty degrees of lon- 
gitude. Whenever, then, the planet happens to be 
situated in one or other of these longitudes, the 
plane of the ring passes through the sun, which 
then illuminates only the edge of it; and as, at 
the same moment, owing to the smallness of the 
earth's orbit compared with that of Saturn, the 
earth is necessarily not far out of that plane, and 
must, at all events, pass through it a little»before 
or after that moment, it only then appears to us a 



very fine straight line, drawn across the disc, and 
projecting out on each side : indeed, so very thin 
is the ring, as to be quite invisible, in this situation, 
to any but telescopes of extraordinary power. 
This remarkable phenomenon takes place at inter- 
vals of fifteen years ; but the disappearance of the 
ring is generally double, the earth passing tivice 
through its plane before it is carried past our orbit 
by the slow motion of Saturn. As the planet, 
however, recedes from these points of its orbit, the 
line of sight becomes gradually more and more 
inclined to the plane of the ring, which, according 
to the laws of perspective, appears to open out into 
an ellipse which attains its greatest breadth when 
the planet is ninety degrees from either node. 




Let S be the sun, ABCDEFGH Saturn's 
orbit, and IKLMNO the earth's orbit. Both 
Saturn and the earth move according to the order 
of the letters, and when Saturn is at A its ring is 
turned edgewise to the sun S, and it is then seen 
from the earth as if it had lost its ring, let the 
earth be in any part of its orbit whatever, except 
between N and 0; for, whilst it describes that 
space, Saturn is apparently so near the sun as to 
be hid in his beams. As Saturn goes from A to C, 
its ring appears more and more open to the earth. 
At C the ring appears most open of all, and seems 
to grow narrower and narrower as Saturn goes 
fi-om C to E ; and when it comes to E, the ring is 
again turned edgewise both to the sun and earth: 
and as neither of its sides are illuminated, it is 
invisible to us, because its edge is too thin to be 
perceptible, and Saturn appears again as if it had 
lost its ring. But as it goes from E to G, its ring 
opens more and more to our view on the under 
side, and seems just as open at G as it was at C ; 
and may be seen in the night-time from the earth 
in any part of its orbit, except about M, when the 
sun hides the planet from our view. As Saturn 
goes from G to A, its ring turns more and more 



WONDERS OF THE HEAVENS 



185 



edgewise to us, and, therefore, it seems to grow 
narrower and narrower ; and at A it disappears as 
before. Hence, while Saturn goes from A to E, 
the sun shines on the upper side of the ring, and 
the under side is dark; and whilst it goes from E 
to A, the sun shines on the under side of the ring, 
and the upper side is dark. 

If we take the dimensions of the ring with a 
micrometer, we shall find that its apparent breadth, 
as has been stated, is equal to the distance of its 
interior border from the surface of the planet. 
This distance is a third of the diameter of the 
planet, and its mean value is 5". 4. The real 
dimensions are probably rather smaller. They 
would naturally appear enlarged on account of 
irradiation. The best telescopes enable us to 
observe on the surface of the ring concentric lines, 
extremely fine and dark, that appear to divide it 
into many parts. There is, therefore, probably 
many distinct rings. The telescope must be very 
powerful to permit us to discover these lines of 
division. With other than powerful instruments 
the whole appears as one ring, increased somewhat 
in brsadth by irradiation. 

These rings cast a deep shadow upon the planet, 
which proves that they are not shining fluids, but 
composed of solid matter. They appear to be 
possessed of a higher reflective power than the 
surface of Saturn, as the light reflected by them is 
more brilliant than that of the planet. One obvious 
use of this double ring is, to reflect light upon the 
planet in the absence of the sun: what other 
purposes it may be intended to subserve in the 
system of Saturn, is, at present, to us unknown. 
It will naturally be asked how so stupendous an 
arch, composed of solid and ponderous materials, 
can be sustained without collapsing and falling in 
upon the planet. The ring has a rapid rotation in 
its own plane, which observation has detected 
owing to some portions of its surface being a little 
less bright than others. 

The period of the ring's revolution presents to 
us quite a singular relation. If a satellite be 
supposed to describe an orbit round the planet, 
having the mean circumference of the ring for its 



24 



circumference, and its sidereal revolution be com- 
puted, it will be found equal to that of the ring. 
This relation answers the question above stated as 
to the manner in which the ring is sustained with- 
out touching the planet ; or it refers the phenome- 
non to the general cause by which all satellites 
are sustained in their orbits. We may view in 
the light of a small satellite each particle of the 
ring, or its whole as a multitude of satellites 
connected inseparable together. If these small 
supposed bodies were independent of each other, 
their velocities would differ according to their 
distances from the centre of the primary. Those 
situated nearest the centre would have the greatest, 
those furthest from the centre the least, velocity ; 
and if we take for the mean term the velocity that 
belongs to the mean circumference of the ring, the 
velocities of the other particles would deviate from 
it each way by equal quantities, the greater coun- 
terbalancing the smaller. Now, if the particles 
were united and attached to each other so as to 
form one solid body, a sort of compensation would 
take place in their motions : the most rapid would 
tend to impart greater rapidity to the slowest, and 
the slowest would tend to retard the motion of the 
most rapid ; and as these efforts would balance each 
other, there would remain the mean motion common 
to all the particles, which would be that of the 
mean circumference, and the rings would be sus- 
tained about Saturn in the same way as the moon 
is sustained about the earth, or like the arches of a 
bridge when the centre of gravity is at the centre 
of the voussoirs. It is the centrifugal force (arising 
from the rotation) which sustains the ring; and 
although no observations nice enough to exhibit a 
difference of periods between the outer and inner 
rings have hitherto been made, it is probable that 
such a difference does exist as to place each, 
independently of the other, in a similar state of 
equilibrium. 

This theory would hold good were the riag 
composed, as that of Saturn's seems to be, of 
several detached and concentric circles, only it must 
be applied separately to each. The periods of 
their rotations would then be different. 



as^EsascEs^ 



■:Bti.*y!! ^jzxrrx!e^7^vrmxr.:r7'='T3faPB^rMianB<Kriw>^ ^ f -H 



WONDERS OF THE HEAVENS 



Although the rings are, as we have said, very 
nearly concentric with the body of Saturn, yet 
recent micrometrical measurements of extreme 
delicacy have demonstrated that the coincidence is 
not mathematically exact, but that the centre of 
gravity of the rings oscillates round that of the 
body, describing a very minute orbit, probably 
under laws of much complexity. Trifling as this 
remark may appear, it is of the utmost importance 
to the stability of the system of the rings. Sup- 
posing them mathematically perfect in their circular 
form, and exactly concentric with the planet, it is 
demonstrable that they would form (in spite of their 
centrifugal force) a system in a state of unstable 
equilibrium, which the slightest external power 
would subvert, not by causing a rupture in the 
substance of the rings, but by precipitating them, 
unbroken, on the surface of the planet. For the 
attraction of such a ring or rings on a point or 
sphere eccentrically situate within them, is not the 
same in all directions, but tends to draw the point 
or sphere towards the nearest part of the ring, or 
away from the centre. Hence, supposing the body 
to become, from any cause, ever so little eccentric 
to the ring, the tendency of their mutual gravity is, 
not to correct, but to increase, this eccentricity, and 
to bring the nearest parts of them together. Now, 
external powers, capable of producing such eccen- 
tricity, exist in the attractions of the satellites, and 
in order that the system may be stable, and possess 
within itself a power of resisting the first inroads of 
such a tendency while yet nascent and feeble, and 
opposing them by an opposite or maintaining power, 
it is sufficient to admit the rings to be loaded in 
some part of their circumference, either by some 
minute inequality of thickness, or by some portions 
being denser than others. Such a load would give 
to the whole ring to which it was attached some- 
what of the character of a heavy and sluggish 
satellite, maintaining itself in an orbit with a certain 
energy sufficient to overcome minute causes of dis- 
turbance, and establish an average bearing on its 
centre. But even without supposing the existence 
of any such load — of which, after all, we have no 
proof — and granting, therefore, in its full extent, 



the general instability of the equilibrium, we think 
we perceive, in the periodicity of all the causes of 
disturbance, a sufficient guarantee of its preserva- 
tion. However homely be the illustration, we can 
conceive nothing more apt in every way to give a 
general conception of this maintenance of equi- 
librium under a constant tendency to subversion, 
than the mode in which a practised hand will sustain 
a long pole resting on the finger in a perpendicular 
position by a continual and almost imperceptible 
variation of the point of support. Be that, how- 
ever, as it may be, the observed oscillation of the 
centres of the rings about that of the planet is in 
itself the evidence of a perpetual contest between 
conservative and destructive powers, both ex- 
tremely feeble, but so opposing one another as to 
prevent the latter from ever acquiring an uncon- 
trollable ascendency, and rushing to a catastrophe. 

This is also the place to observe, that, as the 
smallest difference of velocity between the body 
and rings must infallibly precipitate the latter on 
the former, never more to separate, (for they would, 
once in contact, have attained a position of stable 
equilibrium, and be held together ever after by an 
immense force,) it follows, either that their motions 
in their common orbit round the sun must have 
been adjusted to each other by an external power 
with the minutest precision, or that the rings must 
have been formed about the planet while subject to 
their common orbitual motion, and under the full 
and free influence of all the acting forces. 

The rings of Saturn must present a magnificent 
spectacle from those regions of the planet which lie 
above their enlightened sides. On the other hand, 
in the regions beneath the dark side, a solar eclipse 
of fifteen years in duration, under their shadow, 
must afford (to our ideas) an inhospitable asylum to 
animated beings, ill compensated by the faint light 
of the satellites. But we shall do wrong to judge 
of the fitness or unfitness of their condition from 
what we see around us, when, perhaps, the very 
combinations which convey to our minds only 
images of horror, may be in reality theatres of the 
most striking and glorious displays of beneficent 
contrivance. When viewed from the middle zone 



WONDERS OF THE HEAVENS. 



187 



of the planet, in the absence of the sun, the rings 
will appear like vast luminous arches, extending 
along the canopy of heaven from the eastern to the 
vi^estern horizon, having an apparent breadth equal 
to a hundred times the apparent diameter of our 
moon, and will be seen darkened about the middle 
by the shadow of Saturn. 

The figure beneath presents a view of the appear- 
ance which the rings and moons of Saturn will 
exhibit, in certain cases, about midnight, when 
beheld from a point twenty or thirty degrees north 
from its equator. The shade on the upper part of 
the rings represents the shadow of the body of 
Saturn. The shadow will appear to move gradu- 
ally to the west as the morning approaches. 




There is no other planet in the solar system 
whose firmament will present such a variety of 
splendid and magnificent objects as that of Saturn. 
The various aspects of the seven moons, one rising 
above the horizon while another is setting, and a 
third approaching to the meridian; one entering 
into an eclipse, and another emerging from it ; one 
appearing as a crescent, and another with a gibbous 
phase ; and sometimes the Avhole of them shining in 
the same hemisphere, in one bright assemblage; — 
the majestic motions of the rings, at one time 
illuminating the sky with their splendor, and eclips- 
ing the stars ; at another, casting a deep shade over 
certain regions of the planet, and unveiling to view 
the wonders of the starry firmament; — are scenes 
worthy of the majesty of the Divine Being to unfold, 
and of rational creatures to contemplate. Such 
magnificent displays of wisdom and omnipotence 



lead us to conclude that the numerous splendid 
objects connected with this planet were not created 
merely to shed their lustre on naked rocks and 
barren sands, but that an immense population of 
intelligent beings is placed in those regions to 
enjoy the bounty and to adore the perfections of 
their great Creator. 

HEESCHEL. 

From inequalities in the motions of Jupiter and 
Saturn, which could not be accounted for from the 
mutual action of these planets, it was supposed by 
some astronomers that there existed, beyond the 
orbit of Saturn, another planet, by whose action 
these irregularities were produced. 

This happy conjecture was confirmed on the 
13th of March, 1781, when Herschel discovered 
a new planet, which, in compliment to his patron, 
he named the Georgium Sidus, (the Georgian.) 
It has been called by some Uranus, and by others 
Herschel. This last name has been in popular use 
in this country, and we hope it may ever continue 
to be so. The new planet, which had been pre- 
viously observed as a small star, and introduced 
into catalogues of the fixed stars, is situated beyond 
the orbit of Saturn, at the distance of one thousand 
nine hundred millions of miles from the centre of the 
system, and performs its sidereal revolution round 
the sun in eighty-four of our years nearly, which 
is one year to that planet. Its diameter is more 
than four times that of the earth, being over thirty- 
three thousand miles. As the distance of the 
planet Herschel from the sun is twice as great as 
that of Saturn, it can scarcely ever be distinguished 
by the naked eye. When the sky, however, is 
serene, it appears like a fixed star of the sixth 
magnitude, with a bluish white light, and a bril- 
liancy between that of Venus and the moon ; but 
with a power of two hundred or three hundred, its 
disc is visible and well defined. 

On January 11th, 1787, as Herschel was observ- 
ing this planet, he perceived, near its disc, some 
very small stars, whose places he noted. The next 
evening, upon examining them, he found that two 
of them were missing. Suspecting, therefore, that 



i! ',ttiHiHMyH«r-'- ^'*rw» ^-'*' *' -i^^-"^'"«HW.lW 



188 



WONDERS OF THE HEAVENS 



they might be satellites which had disappeared in 
consequence of having changed their situation, he 
continued his observations, and in the course of a 
month discovered them to be satellites, as he had 
first conjectured. Of this discovery he gave an 
account in 1787. 

In 1788, he published a further account of this 
discovery, containing their periodic times, their dis- 
tances, and the positions of their orbits, so far as he 
was then able to ascertain them. The most con- 
venient method of determining the periodic time of 
a satellite, is, either from its eclipses, or from 
taking its position in several successive oppositions 
of the planet ; but no eclipses have yet happened 
since the discovery of these satellites, and it would 
be waiting a long time to put in practice the other 
method. Dr. Herschel, therefore, took their situa- 
tions whenever he could ascertain them with some 
degree of precision, and then reduced them, by 
computation, to such situations as were necessary 
for his purpose. In computing the periodic times, 
he has taken the synodic revolutions, as the posi- 
tions of their orbits, at the times when their situa- 
tions were taken, were not sufficiently known to 
get very accurate sidereal revolutions. The mean 
of several results gave the synodic revolution of the 
first satellite eight days and seventeen hours, and of 
the second, thirteen days and eleven hours. The 
results, he observes, of which these are a mean, do 
not much differ among themselves, and therefore 
the mean is probably tolerably accurate. 

The next thing to be determined in the elements 
of the satellites was their distances from the 
planet, to obtain which he found one distance by 
observation, and then the other from the periodic 
times. Now, in attempting to discover the dis- 
tance of the second, the orbit was seemingly ellipti- 
cal. On March 18th, 1787, at eight hours, he 
found the elongation to be forty-seven seconds, this 
being the greatest of all the measures he had taken. 
Hence, at the mean distance of this planet from the 
earth, this elongation will be forty-four seconds. 
Admitting, therefore, for the present, says Her- 
schel, that the satellites move in circular orbits, 
we may take forty-four seconds for the true dis- 



tance without much error ; hence, as the squares 
of the periodic times are as the cubes of the dis- 
tances, the distance of the first satellite comes out 
thirty-three seconds. The synodic revolutions were 
here used instead of the sidereal, which will make 
but a small error. 

The last thing to be done, was to determine the 
inclinations of the orbits, and the places of their 
nodes. And here a difficulty presented itself which 
could not be got over at the time of his observation ; 
for it could not be determined which part of the 
orbit was inclined to the earth, and which from it, 
and it is still undecided. So that, we may believe, 
there is an optical illusion in the case, and that these 
secondaries in reality describe their orbits by a 
motion from west to east, preserving unbroken the 
analogy which is found to exist with respect to all 
the other planetary worlds, secondary as well as 
primary. Their orbits are very nearly perpendicu- 
lar to the ecliptic. The six were all discovered by 
Herschel, as well as the planet they accompany, 
and he further suspected, from the result of his 
observations, that the planet was surrounded by two 
rings perpendicular to each other. This, if it were 
established as a fact, would be a very remarkable 
one ; but it cannot be considered as at all certain. 

There are no means, like those used in the case 
of Jupiter and Saturn, of ascertaining the distance 
and actual magnitude of this planet : the determina- 
tion of these elements rests on the observation of 
its periodic time, and the law by which the periodic 
times and the distances are connected. 

According to La Place, the five satellites nearest 
the planet Herschel may be retained in their orbits 
by the action of its equator, and the sixth by the 
action of the interior satellites ; and hence he 
concluded that this planet revolves about an axis 
very little inclined to the ecliptic, and that the 
time of its diurnal rotation cannot be much less 
than that of Jupiter or Saturn. 

When the earth is in its perihelion, and Herschel 
in its aphelion, the latter becomes stationary when 
its elongation or distance from the sun is two 
hundred fifty-seven and a half degrees, and its 
retrogradations continue nearly one hundred and 



Htsasm^Bsz^B 



WONDERS OF THE HEAVENS. 



189 



fifty-two days. When the earth is in aphelion, and 
Herschel in its perihelion, it becomes stationary at 
an elongation of two hundred fifty-six and a half 
degrees, and the retrogradations continue nearly 
one hundred and fifty days. 

The celestial globes which we have now describ- 
ed, are all the planets which are at present known 
to belong to the solar system. It is probable that 
other planetary bodies may yet be discovered be- 
tween the orbits of Saturn and Herschel, and even 
far beyond the orbit of the latter ; and it is also not 
improbable that planets may exist in the immense 
interval of thirty-seven millions of miles between 
Mercury and the Sun. These, if any exist, can 
be detected only by a series of day observations, 
made with equatorial telescopes ; as they could not 
be supposed to be seen after sunset, on account 
of their proximity to the sun. Five primary planets, 
and eight secondaries, have been discovered within 
the last fifty-six years ; and, therefore, we shall have 
no reason to conclude that all the bodies belong- 
ing to our system have been detected, till every 
region of the heavens be more fully explored. 

The plate facing this page is intended to repre- 
sent the relative magnitudes of the seven principal 
planets in the system, the sun's diameter being con- 
sidered as three feet and five inches. Their diamg- 
ters in miles are also appended, as well as their 
mean distances from the sun in millions of miles, 
and the distances of the secondaries from their 
primaries in thousands of miles. 



In closing this section, we will add an illustration 
calculated to convey to the minds of our readers a 
general impression of the relative magnitudes and 
distances of the parts of the system. Choose any 
well levelled field. On it place a globe two feet 
in diameter, which will represent the sun. Mer- 
cury will be represented by a grain of mustard seed, 
on the circumference of a circle one hundred and 
sixty-four feet in diameter for its orbit; Venus a 
pea, on a circle two hundred and eighty-four feet 
in diameter ; the earth also a pea, on a circle of 
four hundred and thirty feet ; Mars a rather large 
pin's head, on a circle of six hundred and fifty- 
four feet; Juno, Ceres, Vesta, and Pallas, grains 
of sand, in orbits of from one thousand to one 
thousand two hundred feet; Jupiter a moderate- 
sized orange, in a circle nearly half a mile across ; 
Saturn a small orange, on a circle of four fifths of 
a mile ; and Herschel a full-sized cherry, or small 
plum, upon the circumference of a circle more 
than a mile and a half in diameter. As to getting 
correct notions on this subject from those toys 
called orreries, it is out of the question. To imitate 
the motions of the planets in the above-mentioned 
orbits, Mercury must describe its own diameter in 
forty-one seconds ; Venus, in four minutes and 
fourteen seconds ; the earth, in seven minutes ; 
Mars, in four minutes and forty-eight seconds; 
Jupiter, in two hours and fifty-six minutes ; Saturn, 
in three hours and thirteen minutes ; and Herschel, 
in two hours and sixteen minutes. 



CHAPTER VI. 



SECTION I. 

Comets — Little knoAvn of their nature or purposes — Their number — 
Comet of 1680 — The tail not an invariable appendage — What are 
the essentials of a comet — How distinguished from a planet — An- 
ciently considered as meteors — Proof to the contrary — Elements 
of a cometary orbit — Motions of a comet — How recognised — Hal- 
ley's comet — Lexell's — Eneke's — Biela's — Do comets affect the 
temperature of our seasons ?— Physical constitution — The envelope 
— Nucleus — Tail — Do comets have phases ? — Variation in the size 
of the envelope. 



Besides the planetary globes of which we have 
treated, there is a class of celestial bodies that 
occasionally appear in the heavens to which the 
name of Comets (hairy stars) has been given. Their 
extraordinary aspect, their rapid and seemingly 
irregular motions, the unexpected manner in which 
they often burst upon us, and the imposing magni- 
tudes which they sometimes assume, have in all 



190 



WONDERS OF THE HEAVENS. 



ages rendered them objects of astonishment not 
unmixed with superstitious dread to the uninstruct- 
ed, and an enigma to those most conversant with 
the wonders of nature and the operations of natural 
causes. Even now that we have ceased to regard 
their movements as irregular, or as governed by 
other laws than those which retain the planets in 
their orbits, their intimate nature, and the offices 
they perform in the economy of our system, are as 
much unknown as ever. No account, to which we 
can give full credence, has been rendered of the 
many singularities that they present. They are 
distinguished from the other heavenly bodies by 
their ruddy appearance, and in general by the 
accompaniment of a long train of light, known by 
the name of the tail, though improperly, since it 
often precedes them in their motions. This train 
sometimes extends over a considerable portion of 
the heavens, and is so transparent that stars may 
be seen through it. The number of comets which 
have been astronomically observed, or of which 
notices have been recorded in history, is very great. 
In a list cited by La Lande, seven hundred are enu- 
merated. When we consider, that, in the earlier 
ages of astronomy, and, indeed, in more recent 
times, before the invention of the telescope, only 
large and conspicuous ones were noticed, and that 
since due attention has been paid to the subject 
scarcely a year has passed without the observation 
of one or two of these bodies, and that in some 
years four and even five have been observed, (two 
or three at once,) it will be readily conceded that 
their number may be many thousands. 

Multitudes, indeed, must escape all observation, 
by reason of their paths traversing only that part 
of the heavens which is above the horizon in the 
daytime. Comets so circumstanced can only be- 
come visible by the rare coincidence of a total 
eclipse of the sun, — a coincidence which happened, 
as related by Seneca, sixty years before Christ, 
when a large comet was actually observed very 
near the sun. Several, however, stand on record 
as having been bright enough to be seen in the day- 
time, even at noon, and in bright sunshine. Such 
were the comets of 1402, and 1532, and that which 



appeared a little before the assassination of Caesar, 
and was supposed to have predicted his death. 

That feelings of awe and astonishment should be 
excited by the sudden and unexpected appearance 
of a great comet, is no way surprising ; being, in 
fact, according to the accounts we have of such 
events, one of the most brilliant and imposing of all 
natural phenomena. Comets consist, for the most 
part, of a large and splendid, but ill-defined, nebu- 
lous mass of light, called the head, which is usually 
much brighter towards the centre, and offers the 
appearance of a vivid nucleus, like a star or planet. 
From the head, and in a direction opposite to that 
in which the sun is situated from the comet, appear 
to diverge two streams of light, which grow broader 
and more diffused at a distance from the head, 
and which sometimes close in and unite at a little 
distance behind it — sometimes continue distinct 
for a great part of their course, producing an effect 
like that of the trains left by some bright meteors, 
or like the diverging fire of a sky-rocket, only 
without sparks or perceptible motion. This is the 
tail. This magnificent appendage attains occasion- 
ally an immense apparent length. Aristotle relates 
of the tail of the comet of 371 A. C, that it occu- 
pied a third of the hemisphere, or sixty degrees: 
that of A. D. 1618 is stated to have been attended 
by a train no less than one hundred and four de- 
grees in length. In the figure of the comet of 1680, 
the most celebrated of modern times, we distinguish 
the nucleus with its surrounding atmosphere or 
nebulosity; above is a sort of half-ring, largest at 
the top, and narrower at the sides ; on the other 
side is an appearance which has been denominated 
a beard; then comes a long tail, in the form of a 
cone, with a light less lively than that of the head. 
This comet, with a head not exceeding in bright- 
ness a star of the second magnitude, covered with 
its tail an extent of more than seventy degrees of 
the heavens, or, as some accounts state, ninety 
degrees. Its length exceeded ninety-six millions of 
miles. 

The tail is by no means an invariable appendage 
of comets. The smallest, such as are visible only 
in telescopes, or with difficulty by the naked eye. 



Et t iMSJLJmx.r T 'mia ^ vsjurjs. ' Ai.s^ vm ai 



^1 1. 1 ■■■ wnKtmrn'm mm^ 



n»JM g ia.BaM g g.j» tBre 



WONDERS OF THE HEAVENS 



191 



and which are by far the most numerous, offer very 
frequently no appearance of such an accompani- 



ment, but appear only as round or somewhat oval 
vaporous masses, most dense toward the centre ; 




and some of the brightest have been observed to 
have short and feeble tails, or to be wholly without 
them. Those of 1585, and 1763, offered no trace 
of such an appendage ; and Cassini describes the 
comet of 1682 as being round and bright like 
Jupiter. 

Every hairy star which passed successively 
through different constellations, was formerly called 
a comet; but modern astronomers give this name, 
notwithstanding its etymology, to bodies that have 
not this hairy appearance. We may define a comet 
by the following characteristics. 1. It must have a 
proper motion, or a motion of its own. 2. It must 
move in a very elongated curve, so that it will pass, 
in certain parts of its course, to such a distance 
from the earth as to be invisible. 

The very elongated form of the orbit makes a 
marked distinction between a comet and a planet. 
When Herschel discovered the heavenly body that 
has since taken his name, it was for some time 
supposed to be a comet, although it had neither 
tail nor hairy appearance, for its proper motion 
among the constellations was manifest ; and, in 
order to explain why it had not before been seen 
and recognised, it was supposed that it had now 
made its appearance for the first time, and that its 
great distance had hitherto rendered it invisible. 
But when it was proved, by careful and continued 
observation, that it passed round the sun nearly in a 
circle, and was visible at all seasons in the absence 
of daylight, it was ranked among the planets. 

Comets were considered by most of the ancient 
philosophers as mere meteors, formed in the earth's 
atmosphere ; but they are now known to be celestial 



bodies. To ascertain this, it was only necessary 
to compare together several observations made at 
the same time in different parts of the earth very 
remote from each other. 

From the time of Tycho Brahe, to whom we are 
indebted for this discovery, comets have been known 
to move round the sun accordmg to certain laws, 
similar to those which regulate the motions of the 
planets, in orbits that are very elongated ellipses, 
the sun being always in one of the foci of the 
ellipse. 

By a calculation, of which it would be impossible 
to give an exact idea in this place, it may be shown 
that three positions of a comet, seen from the earth, 
are sufficient to determine its orbit. The several 
particulars or elejnents which constitute this determi- 
nation are : — 

The inclination of the orbit, and the longitude of 
the node necessary to determine the position of the 
plane of the orbit ; the longitude of the perihelion, 
showing the situation of that curve in its own 
plane; the perihelion dista?ice, which shows the 
form of the orbit, because the focus necessarily 
coincides with the sun's centre ; and last, the 
direction of the motion, expressed by one of these 
words, direct, retrograde. 

To calculate the ele?ne?ds is the first object of 
astronomers when a comet appears. In order to 
do this, three observations are necessary. If only 
two can be obtained, the form and the position of 
its orbit must remain unknown. If many observa- 
tions can be had, they all tend to establish the 
final result, and it is the more exact. 

We come now to speak of the motions of comets. 



192 



WONDERS OF THE HEAVENS 



These are apparently most irregular and capricious. 
Sometimes they remain in sight for only a few days, 
at others for many months ; some move with ex- 
treme slowness, others with extraordinary velocity ; 
while not unfrequently the two extremes of appa- 
rent speed are exhibited by the same comet in dif- 
ferent parts of its course. The comet of 1472 
described an arc in the heavens of one hundred and 
twenty degrees in extent in a single day. Some 
pursue a direct, some a retrograde, and others a 
tortuous and very irregular, course; nor do they 
confine themselves, like the planets, within any 
certain region of the heavens, but traverse indiffer- 
ently every part. Their variations in apparent 
size, during the time they continue visible, are no 
less remarkable than those of their velocity. Some- 
times they make their first appearance as faint and 
slow-moving objects, with little or no tail, but by 
degrees accelerate, enlarge, and throw out from 
them this appendage, which increases in length and 
brightens till (as always happens in such cases) 
they approach the sun, and are lost in his beams. 
After a time they again emerge on the other side, 
receding from the sun with a velocity at first rapid, 
but gradually decreasing. It is after thus passing 
the sun, and not till then, that they shine forth in 
all their splendor, and that their tails acquire their 
greatest length and development; thus indicating 
the action of the sun's rays as the exciting cause of 
that extraordinary emanation. As they continue 
to recede from the sun, their motions diminish, and 
the tail fades away, or is absorbed into the head, 
which itself grows continually feebler, and is at 
length altogether lost sight of, never, in by far the 
greater number of cases, to be seen more. 

Without the clue furnished by the theory of 
gravitation, the enigma of these seemingly irregular 
and capricious movements might ' have remained 
forever unresolved. But Newton, having demon- 
strated the possibility of any conic section whatever 
being described about the sun by a body revolving 
under the dominion of that law, immediately per- 
ceived the applicability of the general proposition 
to the case of cometary orbits; and the great 
comet of 1680, (which we have represented above,) 



one of the most remarkable on record, both for the 
immense length of its tail and the nearness of its 
approach to the sun, (within one sixth of the diame- 
ter of that luminary, or about ninety thousand 
miles nearer than the moon is to the earth,) afford- 
ed him an excellent opportunity for the trial of his 
theory. The success of the attempt was complete. 
He ascertained that this comet described about 
the sun, as its focus, an ellipse of so great an 
eccentricity as to be undistinguishable from a 
parabola, and that in this orbit the areas described 
about the sun were, as in the planetary ellipses, 
proportional to the times. Hence it became a 
received truth, that the motions of the comets are 
regulated by the same general laws as those of the 
planets, the difference of the cases consisting only 
in the extravagant elongations of their ellipses, and 
in the absence of any limit to the inclinations of 
their planes to that of the ecliptic, or any general 
coincidence in the direction of the motions from 
west to east, rather than from east to west, like 
what is observed among the planets. 

For the most part, it is found that the motions 
of comets may be sufficiently well represented by 
parabolic orbits; that is to say, ellipses whose 
axis are of infinite length, or, at least, so very 
long that no appreciable error in the calculation of 
their motions, during all the time they continue 
visible, would be incurred by supposing them 
actually infinite. The parabola is that conic sec- 
tion which is the limit between the ellipse on the 
one hand, which returns into itself, and the hyper- 
bola on the other, which runs out to infinity. A 
comet, therefore, that should describe an elliptic 
path, however long its axis, must have visited the 
sun before, and must again return, unless disturbed, 
in some determinate period : but should its orbit be 
of the hyperbolic character, when once it has pass- 
ed its perihelion, it could never more return within 
the sphere of our observation, but must run off to 
visit other systems, or be lost in the immensity 
of space. A very few comets have been ascer- 
tained to move in hyperbolas, but many more in 
ellipses. These, then, in so far as their orbits can 
remain unaltered by^ the attractions of the planets, 



WONDERS OF THE HEAVENS. 



193 



must be regarded as permanent members of our 
system. 

After learning how much the form of the tail, of 
the envelope, and the nucleus, vary in the course 
of two or three days, as well as the intensity of 
light from all these parts, no one would expect to 
recognise such a body on its second appearance, 
after a lapse of many years, by any description 
founded on those physical characteristics of size, 
form, or brightness. At any rate, no astronomer 
would rely on these marks. They would leave 
them all out of the question, and confine their 
attention wholly to the course of the comet in the 
heavens. 

When three observations have been made of a 
comet, with sufficient exactness, the elements are 
calculated, and then search is diligently made in 
the catalogue of comets, in which the elements are 
recorded, to ascertain whether it is like any of 
those already observed. 

Let us first suppose that all the sets of elements 
contained in the catalogue, or table, differ from 
that of the new comet. We must still refrain from 
drawing any positive conclusion, because observa- 
tion and theory prove that a comet, in passing near 
a planet, may be so perceptibly deranged in its 
course, that the curve it makes after that approach 
cannot be considered as the continuation of the 
curve it was describing before. 

Now let us suppose a contrary case, and that the 
elements of the new comet differ very little from a 
set of elements found in the table, and which belong 
to a comet seen at some former period. In this 
case there is great probability that they are one and 
the same, and that it is the reappearance of a comet 
returning to its perihelion. We say there is great 
probability only, because, mathematically speak- 
ing, it is not impossible that two comets should 
traverse the heavens in two equal curves, and be 
similarly placed. But when we consider that the 
similitude must relate, at the same time, to the in- 
clination of the plane of the orbit, which may vary 
from 0° to 180° ; to the longitude of the node, that 
is, to a number susceptible of taking all possible 

values from 0° to 360°; to the longitude of the 
25 



perihelion, which, in like manner, may vary 360°; 
finally, to the perihelion distance, which, for comets 
already known, is comprehended between twenty 
and four hundred millions of miles; — when we take 
all these particulars into consideration, we can 
scarcely hesitate to conclude that two comets, 
which, at two different epochs, have appeared with 
all these elements nearly the same, are one and 
the same body. Hitherto, at least, we have been 
justified in this inference by the event. 

Having explained that the different circum- 
stances in the proper motion of a comet are the 
only means of recognising it when it reappears, we 
proceed to apply these principles to the only three 
comets whose periodical return has been satisfacto- 
rily determined. 

THE COMET OF 1759, OR HALLEY'S 
COMET. 

In 1682, there appeared a comet, with great 
splendor, and with a tail of thirty degrees in length. 
It was observed by the celebrated astronomer 
Edmund Halley, who calculated its elem.ents from 
its perihelion passage. Having also calculated the 
elements of a comet of 1607, from observations 
made by Kepler and Longiomontanus, and allowing 
for the inaccuracies that must necessarily occur in 
calculating the orbits, and for the errors into which 
the ablest observers are liable to fall when using 
instruments so much less perfect than those of the 
present day, remembering also that the attraction 
of the planets must produce a real change in a 
comet's orbit at each successive revolution, Halley 
came to the conclusion, that, from the great simi- 
larity in the elements, the comets of 1607, and 
1682, were one and the same. 

Here was an interval of seventy-five years. 
Therefore, in going back about that time from 
1607, there ought to have been seen, if Halley's 
conjecture were founded in truth, a similar comet. 
This was actually the case. In 1531, that is, 
seventy-six years before 1607, Apian had observed 
a comet whose course through the constellations 
he watched very attentively. His observations, 
calculated by Halley, gave, as results, elements 



194 



WONDERS OF THE HEAVENS 



which differed very little from those of the comets 
of 1607, and 1682. A comet had been seen also 
in 1456. From the few precise observations in the 
authors of that period, Pingre found the elements 
to be very similar to those of the comets of 1531, 
1607, and 1682. 

Before the year 1456, we find no good observa- 
tions. The chroniclers thought it enough to say 
that a comet was seen in such and such a constel- 
lation. Not a word do they give as to its relative 
position to known stars, or the hour at which it 
was seen. Consequently the elements of the orbit 
cannot be calculated. When this infallible method 
of recognising a comet fails, the period of its revo- 
lution is the only guide that remains. We have 
already seen how much this period varies, and, 
consequently, how uncertain the results must be. 
It is, therefore, with some doubt that we give the 
comet of 1305, that of 1230, the comet mentioned 
by Haly-ben Rodoan in 1006, that of 855, and a 
comet seen in the year 52 before the Christian era, 
as former appearances of that of 1759. As to the 
comet of 1006, the identity may be inferred from 
the similarity of their limits, if not from their ele- 
ments. In 1305, it was termed " the comet of 
terrible magnitude." 

Some have pretended to trace it as far back as 
230 years before the Christian era, when a comet 
is said to have appeared of considerable magnitude 
and brilliancy, shining with a brightness that sur- 
passed the splendor of the sun. It was supposed 
to have signalized the birth of Mithridates. In 
1456, this comet was beheld by all Europe with 
fear and astonishment, partly on account of its 
great brilliancy, and partly because at that time 
the public mind was enslaved by astrological super- 
stitions. 

The Turks were then engaged in a successful 
war, in which they destroyed the Greek empire : 
they, therefore, might have regarded it as an auspi- 
cious omen. The Christians thought that destruc- 
tion was portended by its appearance, especially 
as its tail was turned towards the east. The Pope 
Calixtus regarded it as at once the sign and the 
instrument of divine wrath. He ordered public 



prayers to be offered up, and granted a year's 
indulgence to all who, at the tolling of the noon 
bell, should say three pater nosters, and three ave 
marias, to propitiate the mercy of Heaven. In this 
very circumstance originates the custom, still pre- 
valent in Catholic countries, of ringing the bells 
at noon. The popular terror can scarcely be 
wondered at, for the comet at that time exhibited a 
tail curved like a sabre, sixty degrees in length, or 
two thirds of the distance between the zenith and 
horizon. Its whole appearance was described as 
singularly splendid, and of a vivid brightness. At 
this return, it was in its most favorable position 
relative to the earth and sun for observation of its 
magnitude and brilliancy. 

In the year 1531, it appeared of a bright gold 
color. It pursued the same apparent path through 
the heavens which it traced in 1835. The cele- 
brated Kepler observed it on his return from a 
convivial party on the 26th of September. It con- 
tinued visible about five weeks. 

The identity of the comets of 1531, 1607, and 
1682, could not be doubted, and accordingly Halley 
was encouraged to predict that a comet would be 
visible toward the end of the year 1758, or the 
beginning of 1759, having elements differing but 
little from the three last mentioned. 

So remarkable a prediction could not fail to 
attract the attention of all astronomers, as its ful- 
filment would form a new era in the astronomy of 
comets ; and therefore it was thought advisable, in 
order to convince the most incredulous, to do away 
as far as was possible with the indefiniteness in 
which Halley had very properly left the date of its 
precise return ; for, in his time, it was impossible 
to determine exactly the amount of disturbances or 
perturbations. It became extremely interesting to 
know whether the attractions of the larger planets 
might not materially interfere with its orbitual 
motion. The computation of their influence from 
the Newtonian law of gravity, a most difficult 
and intricate piece of calculation, was undertaken 
and accomplished by Clairaut, who found that the 
action of Saturn would retard its return by one 
hundred days, and that of Jupiter by no less than 



WONDERS OF THE HEAVENS 



195 



five hundred and eighteen, making in all six hun- 
dred and eighteen days. It might be expected, 
therefore, to reach its perihelion about the middle 
of April, 1759. Clairault also gave notice to the 
public, that, being much hurried in his calculations, 
he had not time to consider many smaller causes, 
which might together make a difference of thirty 
days, more or less, in the period of seventy-six 
years. The event justified all he had said, for 
the comet appeared according to the prediction, 
and passed its perihelion, March 12th, 1759, within 
the assigned limits. Its parabolic elements, a little 
changed since its preceding appearance, were such 
as the calculations of Clairault had made them. 

No doubt could now be entertained as to the 
periodical return of Halley's comet. It remained 
to calculate its next appearance. Damoiseau and 
Pontecoulant did not shrink from the immense 
labor. They carried their approximations much 
further than those who preceded them. They even 
calculated the disturbing force of Herschel, the 
existence of which was unknown in the time of 
Clairault. The following is the result obtained by 
Damoiseau. " The interval between the passage 
of the comet through its perihelion in 1759 and its 
approaching return to that point, will be seventy-six 
years and two hundred and thirty-seven days, 
which, reckoned from the 12th of March, 1759, will 
be accomplished on the 4th of November, 1835." 
Pontecoulant fixed it on the 13th of the same month, 
and Lubbock on the 30th of October. 

The comet became visible (being first seen at 
Rome) on the fifth of August, at three o'clock in 
the morning. Its position was at that time in 
right ascension five hours and twenty-six minutes, 
and in declination twenty-two degrees and seventeen 
minutes north. It was seen again on the next 
morning, and had sensibly advanced to the east. 
From about this time the presence of the moon 
interfered with observations, and we hear that the 
comet was next seen at Dorpat, Russia, on the 
20th of August. In this vicinity it was not seen 
until the 31st of August. When first discovered, 
the comet appeared to be merely a faint nebulous 
mass. By the last of August it was nearly circular. 



brightest in the middle, and fading away upon the 
border. On the 11th of October, the train had a 
length of nine degrees. The nucleus had much 
the appearance of one of Jupiter's satellites, but 
with scarcely any sensible magnitude. It passed 
its perihelion on November 15th,* twenty-two hours 
and thirty minutes, Greenwich mean time, and was 
not seen again until January, 1836, emerging from 
the sun's beams. Mr. J. Muller, assistant in the 
observatory at Geneva, discovered the comet on its 
return from its nearest approach to the sun. It was 
very faint. Its situation was precisely in accord- 
ance with the previous calculations of the director 
of the observatory. The assistant directed his tele- 
scope at the minute given toward the spot designat- 
ed by the calculations, and saw the comet really 
make its appearance, and pass across the object 
glass. This was on the morning of the 1st of 
January, 1836, five hours and fifty-six minutes. 
The right ascension of the comet was then sixteen 
hours and eighteen and a half minutes, and its 
declination twenty-four degrees and forty-four 
minutes south. 

The comet was also seen at Ormskirk, on the 
15th and 16th of January, 1836. Its place on 
January 15th, eighteen hours and fifty minutes, was 
noted, and found to be fifteen hours fifty-nine minutes 
and forty-six seconds of right ascension, twenty- 
seven degrees and twenty-two and a half minutes 
of south declination. On the 19th, it was seen 
again by the same observer ; but the haze allowed 
only a momentary glimpse. The comet was so 
faint that it was impossible to see it without a very 
powerful instrument. The place calculated by 
Shatford's Ephemeris for the moment of the above 
observation, is right ascension fifteen hours fifty-nine 
minutes and forty-three and one fifth seconds, and 
south declination twenty-seven degrees twenty-two 
minutes and forty-two seconds — a very near coinci- 
dence. This comet is evidently wasting away. It 
retains nothing of its ancient "terrible magnhude," 
but is quite a modest, unobtrusive body. On its 
next return, in 1912, it will probably not be visible 
without the aid of powerful telescopes. 

* DiflFering about two days from Pontecoulant's calculation. 



196 



WONDERS OF THE HEAVENS 



LEXELL'S COMET. 

Messier discovered a comet in the month of June, 
1770. As soon as three good observations could 
be obtained, the astronomers hastened, as usual, to 
compute its parabolic elements. These elements 
were found to be unlike those of any comet pre- 
viously observed. 

This comet continued to be visible for a long 
while, which gave an excellent opportunity for 
ascertaining how far its last positions agreed with 
the parabola formed by the means of the early 
observations. Strange to say, the disagreement 
was enormous, and could not be got rid of by any 
possible combination of the parabolic elements. In 
this particular case, therefore, hitherto without 
example, the ellipse could not properly be assimi- 
lated to the parabola ; hence the real ellipse must 
be supposed to have a very short transverse axis. 

Accordingly, Lexell found that the comet of 1770 
had described round the sun an ellipse, of which the 
transverse axis was only three times the diameter 
of the earth's orbit, and which corresponds to a 
revolution of five years and a half. He represented 
also all the positions of this body, during the long 
time it was visible, with the exactness of the obser- 
vations themselves. 

There was, however, one great objection to this 
important result : it would seem that the comet of 
1770, with so short a revolution, ought to have 
been frequently seen. Now there was no account 
of it to be found in any catalogue of comets before 
the time of Messier ; nay, more, it has not been 
observed since, although it has been diligently 
sought in those places where, according to the 
elliptic orbit of Lexell, it ought to have appeared. 

It may be easily imagined how many sarcasms 
and jokes, good or bad, were levelled at astrono- 
mers for their lost comet, and how much they were 
laughed at for having supposed that they had found 
out an infallible method of calculating the return of 
these bodies. There was, to be sure, something 
very mysterious in the non-appearance of the 
comet — a real problem to be solved ; for the bright 
light with which it shone in 1770, forbade the 
supposition of its having returned several times 



without being observed. In our day, the whole 
difficulty has been cleared up ; and the laws of 
universal attraction have derived from this circum- 
stance, which seemed at first to invalidate them, 
a new proof of their stability. 

Why ivas not this comet visible every five years and 
a half before 1770 ? Because its orbit was then 
quite different from what it has been since. 

Why has not this comet been seen since 1770? Be- 
cause its passage through the perihelion in 1776 
took place by daylight, and before another return 
the form of its orbit was so changed, that, if the 
comet had been seen from the earth, it would not 
have been recognised. 

Lexell had remarked, that, according to his 
calculation of the elements in 1770, the comet must 
have passed very near Jupiter in 1767, within a 
fifty-eighth part of its distance from the sun ; that 
in 1779, when it was again returning to us, it was, 
towards the end of August, about 500 times nearer 
to that planet than to the sun. So that notwith- 
standing the immense size of the solar globe, its 
attractive force upon the comet was not a two- 
hundredth part of that of Jupiter. Thus it could 
not be doubted that the comet had experienced 
considerable perturbations in 1767 and in 1779; 
but it was still necessary to prove that those per- 
turbations were numerically sufficient to account 
for its non-appearance both before and after 1770. 

The formulas of the fourth volume of the Mecan- 
ique Cdeste give the analytical solution of this 
problem: The actual elliptical orbit of a comet 
being known, what has it before been, and what 
will it be afterwards, in consequence of the disturb- 
ing influence of the planets ? 

Now it is found, by translating these formulas 
into numbers, and substituting the particular ele- 
ments of the comet for the indeterminate letters, 
that, in 1767, before this comet had approached 
Jupiter, the elliptical orbit it described corresponded 
to a revolution about the sun, not of five years, but 
of fifty years ; and that in 1779, when it escaped 
from the sphere of that planet's attraction, the 
orbit was such as to require at least a period of 
twenty years. It results, moreover, from the same 



WONDERS OF THE HEAVENS. 



197 



researches, that, before 1767, during the whole of 
its revolution, the least distance of the comet from 
the sun was four hundred and eighty millions of 
miles; and that, after 1779, this least distance 
became three hundred and fourteen millions of 
miles. This interval is too great for the comet to 
be visible from the earth. 

With respect to the comet of 1770, therefore, 
however strange it may appear, we are nevertheless 
fully justified in saying, that the influence of Jupiter 
in 1767 brought it within our view, and that the 
same influence in 1779 produced a contrary effect, 
and carried it out of our sight. 

ENCKE'S COMET. 

This comet was discovered at Marseilles, Novem- 
ber 26, 1818, by Pons. 

Bouvard presented its parabolic elements to the 
Board of Longitude, on the 13th of January, 1819. 
A member immediately remarked that the results 
of Bouvard's calculation resembled so much the 
elements of a comet observed in 1805, that he 
could not doubt they were one and the same 
comet. 

The periodical return appeared, by this single 
comparison, to be determined beyond all doubt; 
but the length of its period remained unsettled, as 
it was possible, if not probable, that in thirteen 
years this comet might have returned several times. 

It happened, in this instance, as it often does in 
scientific researches, that what appears improbable 
turns out to be true ; for Encke, of Berlin, proved, 
by indisputable calculations, that this comet re- 
quired for its whole course round the sun but twelve 
hundred days, or three years and three tenths. 

But, say those who believe that the time of a 
comet's revolution must necessarily be very long, 
how happens it that this body, which comes to its 
perihelion in less than three years and a half, was 
never observed before 1805 ? The answer is, It is 
a very small comet, its light is feeble, and it cannot 
be seen with the naked eye. This did not account 
satisfactorily for the want of observations in some 
of its returns ; but it was not long before it was 
found that, among the collections of the Academy, 



there were observations of this comet made in 1786 
and 1795. The table of comets contains, more- 
over, the elements of an orbit, at those two epochs, 
so much like those of 1818, that persons who have 
any knowledge of the disturbances to which these 
bodies are liable, can have no doubt of their 
identity. The points of difference, however, were 
sufficiently remarkable to prevent a hasty decision. 

If doubts were entertained as to the length of the 
revolution of this singular body round the sun, on 
account of its performing its elongated orbit in less 
time than some of the planets employ in their 
circular orbits, it is needless now to discuss them. 
The short period of the comet of 1818, is now an 
undisputed fact, for its reappearance in the southern 
hemisphere in June, 1822, took place in the parts 
of the heavens which the calculations had pointed 
out beforehand. The agreement was not less re- 
markable in 1825; and in 1829, the epoch of its 
third predicted return, it appeared in the places 
which Encke assigned for it a year before, with 
only very slight variations. 

This comet has returned twice since 1829, viz. 
in 1832 and 1835. These returns have been applied 
to a valuable purpose, which will be seen by and 
by. Its next return will be in the latter part of 
1838. 

BIELA'S COMET. 

This comet was discovered at Johannisburg, on 
the 27th of February, 1826, by Biela, and ten days 
afterwards at Marseilles, by Gambart. The latter 
calculated the parabolic elements without delay by 
means of his own observations, and immediately 
perceived, on consulting the table of the elements 
of comets, that this was not its first appearance, 
but that it had been already observed in 1805, and 
in 1772. 

It was accordingly necessary to change the para- 
bolic elements into elliptical elements, in order to 
discover the length of the comet's orbit left unde- 
termined by the former. Clausen and Gambart 
undertook this calculation, and each found, in 
nearly the same time, that the new comet made a 
revolution round the sun in about seven years. 



198 



WONDERS OF THE HEAVENS 



This result was adopted without dispute, (for, in 
1826, astronomers were cured of their old notion 
that the revolution of a comet must necessarily be 
very long,) while, from the example of the comet of 
1770, it was deemed imprudent to venture to 
determine the time of the future reappearance of a 
new comet, before all the derangements and per- 
turbations to which it was liable in its whole course 
had been thoroughly studied. The last apparition 
having taken place according to the prediction in 
1832, the next will be in 1838. It is a small 
insignificant comet, without a tail, or any appear- 
ance of a solid nucleus whatever. Its orbit, by a 
remarkable coincidence, very nearly intersects that 
of the earth ; and had the latter, at the time of its 
passage in 1832, been a month in advance of its 
actual place, it would have passed through the 
comet — a singular rencontre, perhaps not unat- 
tended with danger. 

It was this possibility of danger that made Biela's 
comet an object of interest to astronomers, and of 
dread to others. The former calculated its path, 
and found that there would be in reality no danger 
of a contact, and were at rest.* The latter were 
the more convinced that there must be danger, the 
more evidence accumulated to prove the contrary. 
Arago thus concludes his series of facts and argu- 
ments tending to show the needlessness of alarm. 

" The foregoing facts do not differ from those 
which Olbers published in a note, the meaning of 
which has been so strangely mistaken by the public, 
and by several journalists. Shall I be more suc- 
cessful in my endeavors to explain myself? I hope 
so ; but I cannot be very confident, so long as there 
are persons who, believing that the earth will not 
come in contact with the comet or receive any 
direct injury from it, yet think that the comet 
cannot cross the earth's orbit without altering its 
form, as if this orbit were a material substance ; as 
if the parabolic line described by a bomb through 
the air, when discharged from a mortar, could be 
affected in its course by other bombs having formerly 
been projected through the same space." 

* Biela's comet, during its appearance in 1832, was never within 
about _/i/t?/ millions of miles of tlie earth. 



On comparing the intervals between the succes- 
sive perihelion passages of Encke's comet, after 
allowing in the most careful and exact manner for 
all the disturbances due to the actions of the 
planets, a very singular fact has come to light, viz. 
that the periods are continually diminishing, or, in 
other words, the mean distance from the sun, or 
the major axis of the ellipse, dwindling by slow but 
regular degrees. This is evidently the effect which 
would be produced by a resistance experienced by 
the comet from .a very rare ethereal medium per- 
vading the regions in which it moves; for such 
resistance, by diminishing its actual velocity, would 
diminish also its centrifugal force, and thus give 
the sun more power to draw it nearer. Accord- 
ingly, no other mode of accounting for the phenom- 
enon in question appearing, this is the solution 
proposed by Encke, and generally received. It 
will, therefore, probably fall ultimately into the 
sun, should it not first be dissipated altogether — a 
thing no way improbable, when the lightness of its 
materials is considered, and which seems authorized 
by the observed fact of its having been less and less 
conspicuous at each appearance. 

A new element, then, must in future be taken 
into consideration, namely, the resistance which is 
offered to all bodies by a very thin, gaseous sub- 
stance, that fills all space, and is called by common 
consent ether. 

This resistance does not produce any perceptible 
effect upon the planets, on account of their great 
density ; but comets, being for the most part only a 
collection of light vapor, may be greatly retarded 
by it in their motion. To feel the truth of what we 
have just stated with regard to the different effect 
of resistance upon light and heavy bodies, we need 
only compare the very unequal distances to which 
three balls of the same size could be thrown in the 
air, if one were made of lead, another of cork, and 
a third of eider down, supposing they were all pro- 
jected by equal explosions of powder, and received, 
at starting, equal impulses. 

The effect of the resistance of the ether upon the 
whole duration of the revolution of Encke's comet 
round the sun, amounted to about two days, 



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H ^ ^TO^^l* W laJ B WC.^^J B lJ ^■ l ^W l l l .■j f P J (■ J lWi ■ ^ w^J^ ■ WL ^l ■ ^ ,^J T ,jtf y w[Bl llT 



»n 



WONDERS OF THE HEAVENS 



199 



according to the calculations of Encke himself. If 
this influence upon Biela's comet were of the same 
nature, it could not materially affect the results we 
have obtained respecting the least distance of the 
comet from the earth in 1832. 

Do comets affect the temperature of the seasons 1 
This question brings to the recollection the beau- 
tiful comet of 1811, the high temperature of that 
year, the abundant harvest which it produced, and, 
above all, the superior quality of the comet wines. 
We are well aware how much prejudice one may 
have to encounter, in maintaining that neither the 
comet of 1811, nor any other comet yet known, has 
been the occasion of the slightest change in the sea- 
sons on our globe. This opinion is founded on all 
the circumstances of the case ; whil«t the opposite 
belief, however general it may be, is the result of 
vague conjectures, and destitute of any solid basis. 
We shall first state the facts, and then consider the 
theory founded upon them. 

It is said that comets heat our globe by their 
presence. If it be so, nothing is easier than to 
prove it. Are not the thermometers in all obser- 
vatories consulted several times a day? Are there 
not kept in the same places exact accounts of every 
comet that appears? Let us see then whether 
the average temperature of Paris, for instance, during 
the years in which there have been the greatest 
number of comets, exceeds the average tempera- 
ture of those periods in which none of these bodies 
have approached us. The year 1805, with its two 
comets, was one in which the temperature was 
lowest; the year 1808 must be considered a cold 
year, though there have rarely been seen so many 
comets in so few days ; 1829 was a very cold year, 
notwithstanding the appearance of a comet; 1831, 
during which no such body was seen, was much 
warmer than 1819, when there were three comets, 
one of which was very bright. Now, with these 
facts before us, how is it possible to believe that 
comets raise the temperature of the earth ? One 
thing more should be here noticed, and that is, the 
circumstance of cold years being generally cloudy, 
and that, when the heavens are overcast, the most 
brilliant comets may pass without being perceived. 



Let us now put aside these results of observation, 
for they are still too few for the consequences 
deduced from them to be beyond the reach of objec- 
tion, and look at the problem in another point of 
view. A comet can act from a distance upon the 
earth in three several ways only: by means of 
attraction, by the rays of light and heat which it 
radiates or reflects in all directions, and by the 
gaseous matter that composes its envelope or its 
tail, which, in certain positions, may mix with the 
atmosphere of the earth. The comet of 1811 had 
a very brilliant tail, the extent of which was varia- 
ble. Its greatest length was found by calculation 
to be one hundred millions of miles. Without 
taking the trouble to examine whether this tail 
was ever directed toward the earth, we may safely 
assert that it never touched it, for on the 15th of 
October, when it was nearest, it was at least one 
hundred and fourteen millions of miles from us. 

At the time of its greatest brilliancy, the comet of 
1811 did not certainly afford a light equal to a tenth 
part of that of the full moon ; and the light of the 
full moon, even when concentrated by the focus of 
the largest mirror and lenses, and acting upon the 
blackened bulb of an air thermometer, has never 
produced any sensible effect, although, from the 
manner in which this experiment has been con- 
ducted, a hundredth part of a degree [centigrade] 
would have been readily appreciated. We must 
reject the use of reason, if, with such a result before 
us, we could entertain the idea that a comet, even 
ten times more brilliant than that of 1811, could, 
by its light, produce upon the earth such variations 
of temperature as would affect the quantity or 
quality of its crops, or even such minute changes as 
are capable of affecting our most delicate meteor- 
ological instruments. It must then be in the comet's 
power of attraction that we are to look for the effi- 
cient cause of its meteorological influence. Here 
the moon will serve as a standard of comparison. 

This planet causes the tides of the ocean. Math- 
ematically speaking, the comet of 1811 ought to 
have produced similar tides ; but none such were 
perceived, and therefore it must be admitted that 
they were inappreciable. 



200 



WONDERS OF THE HEAVENS 



The height of the tide varies in proportion to the 
intensity of the attractive force. We have just 
found that the lunar tide is very great, and the 
cometary tide imperceptible : therefore the action 
of the comet upon the earth is but a very small 
part of that of the moon. This important result is 
deduced still more clearly from an examination of 
the disturbance which takes place among the 
planets in their elliptical orbits, and which are 
known by the name of perturbations. We shall 
confine ourselves to the aerial tides. 

The attractive force of the moon cannot fail to 
produce an atmospherical tide, the variations of 
which would be indicated by the barometer. But 
in this case, amid so many accidental causes of dis- 
turbance, the only way of ascertaining the effects 
of the constant action of the moon is to bring 
together several thousand observations. This labo- 
rious and minute calculation has been made, with 
the greatest care, upon observations collected from 
various places ; and the effect of the moon upon the 
atmosphere has scarcely been sufficient to produce 
a perceptible variation in the barometer. We need 
hardly add, after this, that it has never entered any 
body's head to try the effect of a comet upon this 
aerial tide. 

We repeat, that the direct action of the tail and 
the nebulous head of the great comet of 1811 on 
the earth's atmosphere was insensible, on account 
of the immense distance at which this comet has 
always been from the earth. As to its power of 
heating or attracting our globe, the most delicate 
instruments cannot detect its existence. 

Many comets have no perceptible tail; some 
have been seen in which no nucleus could be dis- 
covered; but none have ever been visible, since 
they have been attentively examined with the tele- 
scope, which had not that sort of foggy appearance 
or nebulous atmosphere called by astronomers the 
envelope or chevelure. 

Among the comets that have no apparent nucleus, 
and which seem to be only globular masses of vapor, 
slightly condensed towards the centre, we shall 
notice those of 1795, 1797, and 1798, observed by 
Olbers, and the little comet of 1804, the envel- 



ope of which was forty-eight hundred miles in 
diameter. 

Seneca remarks, that stars may be seen through 
comets. This assertion cannot be called in ques- 
tion, so far as comets without any proper nucleus 
are concerned. It may even be added, that the 
nebulous matter which forms the envelope is so thin 
and transparent that the light of very small stars 
may pass through it to a great distance without 
ceasing to be visible. 

For instance, Herschel saw a star of the sixth 
magnitude in the very middle of the comet without 
a nucleus of 1795; also, on the 28th of November, 
1828, Struve plainly distinguished a star of the 
eleventh magnitude through the central part of 
Encke's comet. Many more such examples might 
be given. 

When there is a nucleus in the centre of a comet, 
it seldom happens that the nebulous envelope 
extends to it with a progressively increased inten- 
sity; on the contrary, that part of the envelope 
nearest the nucleus is faintly illuminated, and 
appears to be extremely rare and transparent. At 
some distance from the centre the envelope becomes 
suddenly brighter, so that it looks like a luminous 
ring, more or less extended, surrounding the 
nucleus, and maintaining itself at a nearly equal 
distance from it on all sides. Sometimes there have 
been seen two and even three of these concentric 
rings, separated by spaces more feebly illuminated. 
It will be easily conceived, that what appears to 
the eye to be a ring is really a spherical envelope; 
and we shall have a good idea of this complicated 
structure of comets, if we imagine, at different 
heights in our atmosphere, three strata of clouds 
completely encircling the globe. To make the 
similitude more exact, we must suppose these three 
strata to be transparent, and yet possessed of 
optical properties different from the intervening 
portions of pure air. 

In the comet of 1811, the envelope could not be 
less than twenty-four thousand miles thick, and its 
interior surface must have been twenty-nine thou- 
sand miles from the centre of the nucleus. The 
envelopes of the comets of 1807 and 1799, were 



saasaaiss3XimsjsssK 



WONDERS OF THE HEAVENS 



respectively twenty-nine thousand and nineteen 
thousand miles thick. 

It is, in all probability, to the feeble coercion of 
the elastic power of their gaseous parts, by the 
gravitation of so small a central mass, that we must 
attribute this extraordinary development of the 
atmospheres of comets. If the earth, retaining its 
present size, were reduced, by any internal change, 
(as by hollowing out its central parts,) to one thou- 
sandth part of its actual mass, its coercive power 
over the atmosphere would be diminished in the 
same proportion, and in consequence the latter 
would expand to a thousand times its actual bulk, 
and indeed much more, owing to the still farther 
diminution of gravity, by the recess of the upper 
parts from the centre. 

The nucleus of a comet generally resembles a 
planet in form and brilliancy. It is commonly very 
small, but sometimes it approaches the dimensions 
of the lesser planets. 

Some astronomers maintain that the nucleus of a 
comet, even when from its brilliant light it most 
resembles a planet, is always transparent ; that 
comets are, in short, nothing but masses of vapor. 
The observations on which this opinion is founded 
are specious enough ; but they do not warrant such 
conclusions as have been drawn from them. The 
question is an important one. Its solution must 
decide, in a great measure, the degree of influence 
to be attributed to comets in the physical revolu- 
tions of the world. 

All comets pass successively in their proper 
motions through different constellations ; but the 
regions in which these movements take place, are 
vastly nearer to us than to the stars. Now it would 
seem evident that if the nucleus of a comet is 
interposed between the observer and a star, we 
can judge better of its intimate constitution than in 
any other position. 

Unfortunately these conjunctions are extremely 

rare, and for the very simple reason, that the part 

of the firmament which is the most crowded with 

stars contains incomparably more void than occupied 

space. Instances, however, are not wanting of such 

conjunctions. 

26 




On the 23d of October, 1774, Montaigne saw, at 
Limages, a star of the sixth magnitude through the 
nucleus of a little comet. 

This observation would undoubtedly prove that 
the comet of 1774 had no solid or opaque part, if 
the star had been seen through the middle of it ; 
but Montaigne does not mention this last circum- 
stance, and indeed the feeble powers of his tele- 
scope would scarcely admit of his being thus 
explicit. 

On the first of April, 1796, Olbers saw a star of the 
sixth or seventh magnitude ; and, though covered by 
a comet, its light was not sensibly diminished. But 
this celebrated astronomer protests against the con- 
clusion which some drew from his observation as to 
the transparency of the nucleus. According to his 
conjectures, the star was situated a little to the 
north of the centre of the envelope, and if the 
nucleus disappeared for a time, it might be only in 
consequence of the neighborhood of the greater 
light of the fixed star. 

The same doubts may be entertained with regard 
to the passage, without a real occultation, of a star 
of the seventh magnitude, behind the nucleus of the 
comet observed at Nismes, in 1825, by Valz ; also 
with regard to former observations of the same kind. 

If we wished to maintain the opinion that there 
is a solid and opaque centre to the luminous nucleus 
of comets, the annals of astronomy would furnish 
us with sufficiently plausible arguments. When 
Messier perceived, for the first time, the little 
comet of 1774, there was, very near its nucleus, 
one telescopic star only, and some hours after a 
second star was seen near the first. This second star 
was not less brilliant than the first, and there is 
but one way of explaining why Messier did not see 
it before : we must admit with him that it was con- 
cealed behind the opaque part of the comet. On 
the 28th of November, 1828, at half past ten at 
night, Encke's comet, which returns to its perihelion 
every three years and a third, was observed by 
Wartmann, at Geneva, to pass over a star of the 
eighth magnitude, which was entirely eclipsed. 
Now a positive fact, like this real disappearance, 
may always be opposed with advantage to a nega- 



202 



WONDERS OF THE HEAVENS 



tive fact, to a non-disappearance, because the latter 
may be always explained without difficulty by a 
supposition fairly admissible, that the small nucleus, 
which is solid and opaque, did not pass exactly over 
the star, however it might have appeared to do so, 
whilst a total eclipse cannot be subject to any such 
uncertainty. 

To be sure, Wartmann used too small a telescope, 
and a magnifier not sufficiently powerful. And 
Messier's observation would be much more con- 
vincing, if he had seen the star before it was 
eclipsed : if the astronomer, aware of its existence, 
had looked for it, we might not then suppose that 
it had escaped him through inattention. Whatever 
may be deduced from these remarks as to the 
constitution of the nucleus of very small comets, 
which we have spoken of as passing over stars, no 
general consequences can be inferred from them. 
There are comets that have no apparent nucleus, 
and are equally bright throughout their whole 
extent, and which are, beyond all doubt, simple 
collections of gaseous matter. An increased degree 
of concentration in these vapors may form a nu- 
cleus in the centre of the head, remarkable for the 
intensity of its light; but this, being still liquid, 
may be very transparent. At a later period, this 
liquid may cool down till it becomes surrounded by 
a solid crust, and then all transparency of the 
nucleus will have ceased. If, after this, it should 
pass between an observer and a star, it would 
cause an eclipse as real and as entire as that which 
is produced by the moon and planets. Now nothing 
is known which goes to prove that there may not 
be comets of this third class with a solid nucleus. 
The great variety in appearance and in brightness 
which these bodies exhibit, will justify any supposi- 
tion of the kind. Those who, since the observa- 
tions of the last forty years, can believe that all 
comets are formed on one model, need only exam- 
ine the archives of science to perceive how little 
such an idea is founded on fact. 

Among the representations of comets given by 
Hevelius, there are two of the comet of 1661, pre- 
senting quite a curious phenomenon. One figure 
shows the nucleus as a single round body, which 



it appeared to be at one observation. The other 
view represents the same comet when its nucleus 
seemed to have separated into several small bodies. 




In the year 43 before Christ, we are told that 
a hairy star appeared which could be seen hy day- 
light with the naked eye. This comet was consider- 
ed by the Romans as the metamorphosis of the soul 
of Caesar, who was assassinated a short time before. 

In the year 1402 after Christ, we hear of two 
very remarkable comets. The first was so bright 
that the light of the sun, towards the end of March, 
did not prevent its nucleus, or even its tail, from 
being seen at noon. The second was visible in the 
month of June, and could be seen long before 
sunset. 

Cardan relates, that, in 1532, the curiosity of the 
inhabitants of Milan was greatly excited by a star 
which could be seen at mid-day. At the time, 
Venus was not in a position in which it could be 
seen by daylight : the star of Cardan must there- 
fore have been a comet. This is the fourth 
visible by daylight recorded by historians. 

The beautiful comet of 1577, was discovered the 
13th of November, by Tycho Brahe, from his 
observatory in the island of Hwen, in the Sound, 
before sunset. 

On the 1st of February, the comet of 1744 was 
more conspicuous than the brightest star in the 
heavens, that is, than Sirius; on the 8th, it equalled 
Jupiter ; some days afterwards, it was only sur- 
passed by Venus ; at the beginning of the next 
month, it was visible by daylight. On the 1st of 
March, several persons, conveniently situated. 



WONDERS OF THE HEAVENS 



203 



perceived this comet, without the aid of glasses, an 
hour after noon. 

What ground, then, is there for comparing, as 
to physical structure, bodies of such brilliancy as 
those just mentioned, and the comets observed 
during the last fifty years, vehich are rendered 
almost entirely invisible by the feeble light which is 
brought into the field of the astronomical telescope, 
in order to show the cross-threads necessary ;to 
determine its position ? 

We may now conclude that there are, 

Comets without a nucleus ; 

Comets of which the nucleus may he transparent ; 

Comets more brilliant than the planets, the 
nucleus of which is probuhly solid and opaque. 

Peter Apian says, after attentively observing the 
comet of 1531, that the tail, whatever may be the 
situation or motions of the comet, is always in the 
prolongation of the line which joins the sun and the 
nucleus. 

This statement is not strictly correct. It is true 
that the tail is generally behind the comet as viewed 
from the sun; but the line which joins the two 
bodies, hardly ever coincides exactly with the axis 
of the tail. Sometimes the difference in the two 
lines is considerable : cases might be mentioned, 
indeed, in which they form a right angle. It is 
found, moreover, that the tail constantly inclines 
towards the region which the comet is leaving, as if, in 
its motion through a gaseous medium, the matter of 
which the tail is composed experienced more re- 
sistance than the nucleus. • This is sometimes so 
great as to produce a very perceptible curvature. 
The tail of the comet of 1744, for instance, formed 
nearly a quarter of a circle in an extent of only a 
small number of degrees. 

If this be the real cause of the curvature of the 
tail, it follows, as a necessary consequence, that 
the convexity must always be turned towards that 
region to which the comet is tending. One or two 
exceptions to this rule may perhaps be found. 

According to the hypothesis under consideration, 
the nebulous matter of the tail must be more con- 
centrated, more dense, and consequently more 
luminous, and the outline must be better defined, 



on the convex side than the other. All known ob- 
servations tend to confirm the truth of this position. 

The tail of a comet becomes larger the further it 
is from the head. The middle often presents a dark 
space, which divides it longitudinally into two dis- 
tinct and often nearly equal parts. Former ob- 
servers considered this dark space as the shadow 
of the body of the comet This explanation, how- 
ever, is not applicable to tails that are not in a line 
with the nucleus and the sun. It is more accordant 
with all the particulars of this phenomenon, to con- 
sider the tail as a hollow cone, the sides of which 
have a certain degree of thickness. For the line of 
sight, in passing through the edges of the cone, will 
strike a great many more nebulous particles, than a 
line through the middle : now, whether these parti- 
cles shine of themselves, or only reflect the rays of 
the sun, it is their whole number which must, in 
every direction, determine the intensity of the light. 
Thus the hypothesis of the hollow cone does away 
all the difficulty respecting the edges of the tail 
being the brightest, and respecting its division into 
two luminous portions, by a comparatively dark 
space. 

The tail of the great comet of 1680, immediately 
after its perihelion passage, was found by Newton 
to have been no less that twenty millions of leagues 
in length, and to have occupied only two days in 
its emission from the comet's body: a decisive 
proof this of its being darted forth by some active 
force, the origin of which, to judge from the direc- 
tion of the tail, must be sought in the sun itself. 
Its greatest length amounted to forty-one million 
leagues, a length much exceeding the whole inter- 
val between the sun and earth. The tail of the 
comet of 1769, extended sixteen million leagues, and 
that of the great comet of 1811, thirty-six million. 
The portion of the head of this last comprised 
within the transparent atmospheric envelope which 
separated it from the tail, was one hundred and 
eighty thousand leagues in diameter. It is hardly 
conceivable that matter once projected to such 
enormous distances should ever be collected again 
by the feeble attraction of such a body as a comet 
— a consideration which accounts for the rapid pro- 



204 



WONDERS OF THE HEAVENS. 



gressive diminution of the tails of such as have been 
frequently observed. 

It is not uncommon for comets to have several 



separate tails. That of 1744, on the 7th and 8th 
of March, had no less than six, each about four 
degrees broad, and from thirty degrees to forty-four 




degrees long. Their edges were well defined, and 
bright : the middle portions emitted a very faint 
light. The space between these separate tails was 
as dark as the rest of the heavens. At the moment 



when the drawing was made, the head of the 
comet was below the horizon. The dotted lines 
indicate the invisible part of the six branches. 
Do comets shine by their own light, or do they, 



WONDERS OF THE HEAVENS. 



205 



like the planets, only reflect the rays of the sun ? 
It will be allowed that this is a most important 
question. It has, however, never been settled. 
We might state, on the faith of certain observations 
of Cassini, that the comet of 1744 exhibited such 
a phase ; but to this it might be replied, that the 
words of that astronomer prove that the nucleus 
was very irregular, not that it had a proper phase. 
Heinsius and Chezeaux, say positively that no phase 
existed at the very time ; and the observations of 
the English geometrician Dunn were contradicted 
by the contemporary observations of Messier. Yet 
the absence of phases in a nucleus surrounded, as 
that of a comet is, with a thick atmosphere, capable 
of disseminating the light on every side, cannot 
lead to any certain conclusion. The recent labors 
of philosophers have given rise to a new mode of 
investigating this subject, which promises more 
valuable results. They have discovered, that when 
light is reflected under certain angles, it is dis- 
tinguished by some peculiar properties from light 
that comes to us directly. Now some traces of 
these peculiar properties have been perceived, at 
the observatory in Paris, in the light from the tail 
of the comet of 1819, but not so distinctly as to 
warrant a positive conclusion that these bodies shine 
only by a borrowed light, for bodies that become 
self-luminous do not lose the power of reflecting 
light received from other sources. 

The nebulous envelopes of comets, when closely 
studied, present inexplicable difficulties. It is very 
natural, to be sure, to suppose them masses of 
permanent gas, or collections of vapor disengaged 
from the nucleus, upon which the solar rays are 
constantly acting; but what becomes, upon this 
supposition, of the luminous, concentric envelopes 
of which we have spoken ? Why should the nucleus 
be eccentric, generally towards the sun, but some- 
times on the opposite side ? 

Wholly occupied with the motions of comets, 
and carried away perhaps by favorite theories, 
modern astronomers have neglected one observa- 
tion, worthy of note, as to the manner in which the 
envelopes of comets vary in size. Hevelius, who 
was bound to no system, stated distinctly that the 



real diameter of the envelope increased according 
as the comet became more distant from the sun. 
Pingre observed this, also, but hardly dared to avow 
it ; for in his work, this important fact is thrown 
out, as if by chance, in a paragraph upon the varia- 
tions of the tail. 

Thanks to Encke's comet, we may now place 
the observation of Hevelius among the best estab- 
lished facts of science. 

On the 28th of October, this comet was nearly 
three times as far from the sun as on the 24th of 
December ; nevertheless, at the former of these 
two periods, the real diameter of the nebulous 
matter was about twenty-five times as great as at 
the latter ! Or we may put the same thing into 
other words, by saying that, in the interim between 
the 28th of October and the 24th of December, 
the size or volume of the comet was reduced to a 
sixteen thousandth part of its former size : the least 
bulk thus corresponds to the least distance of the 
comet from the sun. 

Valz supposes that the ethereal matter forms a 
true atmosphere about the sun, in which the lower 
strata are so much the more compressed, and so 
much the more dense, according as there are a 
greater number of strata above them. He imagines, 
therefore, that the comet, in traversing these 
strata, must imdergo a pressure proportional to their 
density! There would be no objection to this, if it 
were proved that the exterior envelope of nebulous 
matter was not permeable to the ether. It is 
indeed well known, that a bladder, filled with air 
at the base of a mountain, expands as it is raised to 
higher positions, and that it finally bursts when 
carried to a suflScient height. But have we dis- 
covered about the nebulous matter any case or 
pellicle, which will allow us to make the compari- 
son, which would prevent the ether from penetrating 
it in every direction ? This difficulty appears at 
present insurmountable, and we cannot but regret 
it ; for the ingenious hypothesis of Valz gives the 
law of variation for the magnitude of the nebulous 
matter, both for Encke's comet, and for that of 
1618, with an exactness truly surprising. 

It is very possible, however, that the change 



206 



WONDERS OF THE HEAVENS 



may consist in no real expansion or condensation of 
volume, (further than is due to the convergence or 
divergence of the different parabolas described by 
each of its molecules to or from a common vertex,) 
but may rather indicate the alternate conversion of 
evaporable materials in the upper regions of a 
transparent atmosphere, into the states of visible 
cloud and invisible gas, by the mere effects of heat 
and cold. 

It would require a volume to give even a faint 
idea of the great variety of theories by which 
astronomers and philosophers have endeavored to 
explain the tails of comets. The least objection- 
able of these theories is that which supposes the 
lightest particles of the nebulous matter to be de- 
tached and carried off by the force of the sun's rays. 
Accordingly the tail would always be directly op- 
posite to the sun, as Apian would have it. But this 
rule does not apply universally, for the tail is some- 
times perpendicular to the line drawn from the sun 
to the nucleus. It is also occasionally very much 
curved. There are sometimes six tails at once. 
These multiplied tails appear and disappear in u 
few days, and their direction is so various that, hi 
certain positions of the earth, the comet of 1823 
appeared for several days to have one tail extended 
toward the sun, and another in the opposite direction. 
There are indications in these multiplied tails of a 
very rapid rotary motion, which must soon occa- 
sion their entire dispersion in space. There are 
comets, too, the nebulous matter of which seems 
very light, and which nevertheless have no tails at 
all. The resistance of the ether, which has hitherto 
been overlooked, may explain some of these diffi- 
culties ; but it is to be feared that the complete 
solution of so intricate a problem will long be 
wished for in vain. 

Those who take an interest in comets only with 
a view to satisfying themselves whether, in striking 
the earth, they will produce great disasters, must 
find, in the telescopic observations of which we 
have given some account, strong reasons for feeling 
secure. We may also add, that these observations 
are not the only means of ascertaining the ordinary 
smallness of the mass of these bodies; the same 



result is arrived at by studying attentively the 
motions of planets, near which comets have passed. 

The comet of 1770 came very near the earth's 
orbit.* La Place discovered that the action of the 
earth upon it increased the length of its revolution 
by more than two days. Mathematically speaking, 
the reaction of this comet upon the earth ought to 
have increased the length of the earth's revolution 
round the sun. If we suppose the mass of the 
comet to be equal to that of the earth, the time 
thus added to the year would be, by strict calcula- 
tion, two hours and fifty-three minutes. Now it is 
well known that in 1770 the length of the year 
did not vary one second. We have taken, then, for 
the ground of our calculations a very exaggerated 
statement, in supposing the mass of this comet to 
be equal to that of the earth ; and we may fairly 
infer from the above fact, that the mass or quantity 
of matter in the comet is not one five-thousandth 
part of that of the earth. This result explains 
how it was possible for the comet of 1770 to 
traverse twice the system of Jupiter's satellites 
without producing the slightest disturbance. 

We shall conclude this section by a table contain- 
ing the smallest distances from the earth's orbit of 
the comets which have approached the nearest to 
it. It will be easily seen that the same numbers 
would also express the least distances from the 
earth, to which these bodies have ever been able 
to approach. 



Comet of 1680, 


Least distance from the Earth's orbit. 

112 semi-diameters of the earth 


Comet of 1684, 


215 




a 


Comet of 1805, 


260 




a 


Comet of 1742, 


330 




a 


Comet of 1779, 


346 




a 



Let us remember now, that Biela's comet passed 
within about four terrestrial semi-diameters or two 
diameters of the earth's path ; and we shall per- 
ceive that such a circumstance, if it justified none 
of the fears which were excited, deserved at least 
to be noted. 

* The shortest distance of the comet of 1770 from the earth, was 
368 semi-diameters of the earth, or 1,456,840 miles; the mean distance 
of the moon is 60 semi-diameters of the earth, or 237,160 miles. Thus, 
at the nearest approach of the comet of 1770, it was still six times as 
far from us as the moon. 



WONDERS OF THE HEAVENS 



207 



SECTION II. 

Chances against a comet's striking the earth — Do they finally fall 
into the sun ? — Or into the stars ? — Can the earth draw off the tail of 
a comet ? — The effects — Were the fogs of 1783 and 1831 caused by 
a comet ? — Was the cholera caused by a comet ? — The deluge not 
caused by a comet — Has the climate of Siberia suddenly changed ? 
— Is the severe climate of North America owing to a comet ?— Is 
the depression in the centre of Asia owing to a comet? — Was the 
moon ever a comet ? 

In virtue of first causes, the nature of which is un- 
known to us, and which have given rise to various 
theories more or less plausible, the planets of our 
system make their revolutions round the sun all in 
the same direction, and in orbits nearly circular. 
Comets, on the contrary, travel in very elongated 
ellipses, and move in all possible directions. In 
coming from their aphelions, they continually 
traverse our solar system, passing within the orbits 
of the planets, sometimes even between Mercury 
and the sun. It is not, therefore, impossible for a 
comet to encounter the earth. 

The probability of such an event is extremely small. 
This will be evident at first sight, if we compare 
the immense space in which our globe and the 
comets move, with the very small size of these 
bodies. Mathematical calculation carries us much 
further. It gives us, in numbers, the chances for 
or against the event in question, founded on the 
relative magnitude of the comet and the earth. 

Suppose, now, a comet of which we know 
nothing but that, at its perihelion, it will be nearer 
the sun than we are, and that its diameter is equal 
to a quarter of that of the earth ; the doctrine of 
chances shows that, out of two hundred and 
eighty-one millions of cases, there is but one 
against us — but one in which the two bodies could 
meet. 

Here the chances of a collision between the 
earth and the comet are given, without any thing 
being known of the form or position of the comet's orbit. 
There is for the nucleus, properly so called, one 
chance of its striking the earth, one unhappy 
chance, to two hundred and eighty-one million, 
chances of its escaping us ; and for the nebulous 
head, according to its ordinary dimensions, about 
ten or twenty chances in favor of a contact to the 



same number of two hundred and eighty-one mil- 
lions against it. 

At the time of passing its perihelion, the comet 
of 1680 was separated from the sun by a space not 
greater than a sixth part of the diameter of that 
luminary. In a region thus near to that immense 
orb, the atmosphere by which it is surrounded may 
have an appreciable density, producing upon a 
body that passes through it such effects as ought to 
be taken into consideration, particularly in regard 
to comets, the swiftness of whose motion at their 
perihelion is very great, and whose density is 
generally very small. The inevitable effect of this 
atmospheric resistance upon the comet of 1680, 
must have been to diminish its tangential velocity. 
But when a heavenly body slackens its pace, what- 
ever may be the cause, the centrifugal force lessens 
also; the centripetal force, which it counterbal- 
anced, preponderates immediately, and that body 
quits the curve it was describing to approach 
nearer to the centre of attraction. Thus the comet 
of which we have been speaking must have passed 
nearer the sun's surface in 1680 than at its former 
appearance. This diminution in the dimensions of 
its orbit must occur at each return to the peri- 
helion; the comet of 1680 must, therefore, in the end, 
fall into the sun. 

This reasoning is founded on incontestable 
mechanical principles; therefore the consequence 
deduced is not less certain. We must only bear 
in mind that our ignorance of the density of the 
several successive strata of the solar atmosphere, 
of that also of the comet of 1680, and of the 
length of its revolution, renders it impossible to 
calculate how many ages must elapse before this 
strange event is to take place. The annals of 
astronomy furnish us no reason for supposing that 
such a thing has ever happened within the period 
of authentic history. 

Pliny mentions a star, which appeared suddenly 
in the heavens, in the time of Hipparchus (that 
is, two thousand years ago,) and suggested to 
this great astronomer the idea of that catalogue 
of stars for which science is so much indebted 
to him, and which was preserved by Ptolemy. 



208 



WONDERS OF THE HEAVENS. 



Similar phenomena occurred in the years 1572, and 
1604. 

The new star of 1572 appeared on the 8th of 
November, in the north, in the constellation Cas- 
siopeia. It was more conspicuous than the bright- 
est star in the heavens, that is, than Sirius; it gave 
almost as much light as the planet Venus, ^nd was 
visible for nearly a year and a half. That of 1604, 
when seen by the disciples of Kepler, on the 30th 
of September, at noon, in the constellation Ser- 
pentarius, surpassed Jupiter in splendor, though 
the night before it appeared very small. At the 
end of sixteen months there was no trace of it to 
be seen. 

Fixed stars are real suns, around which, in all 
probability, planets and comets revolve. The facts 
just stated prove that there are, besides the com- 
mon stars, exhausted or extinguished stars, that 
are ordinarily invisible. Newton believed that this 
kind of stars again become conspicuous, and sud- 
denly recover their former brilliancy, when comets, 
by falling into them, furnish them with fresh com- 
bustible matter. 

If this explanation were adopted, it would follow, 
that within the period of authentic history, comets 
had, in three instances, fallen, if not into the still 
brilliant sun of our system, at least into the extinct 
suns of other systems. 

By comparing the fires of the heavenly bodies 
with those of our own kindling, and considering 
comets like the billets of wood, which must be con- 
stantly renewed upon our hearths, we carry the 
laws of analogy much too far. It is now generally 
known, that, under certain specific conditions, and 
particularly in certain electrical states, all bodies 
may become luminous, without any thing combining 
with their substance, and without any thing being 
disengaged from them. This is the case with two 
pieces of charcoal, placed in a vacuum, one of which 
touches a wire connected with one end of a power- 
ful galvanic battery, whilst the other communicates 
with the opposite end. As soon as the surfaces of 
the two coals are brought near each other, they 
become more resplendent than any other known 
terrestrial fire, so much so, that it is agreed to 



distinguish the light thus produced by the name 
of solar light. 

Newton thought that the matter, the exhalation, 
of which the tails of comets are composed, might 
fall by its gravity into the atmosphere of any 
planet, but more especially into that of the earth, 
be condensed there, and give rise to all sorts of 
chemical reactions, and a thousand new combina- 
tions. 

Comets appear to be, for the most part, mere 
collections of vapor. Now since it is an incontesta- 
ble principle that attraction is in proportion to the 
mass or quantity of matter, each particle of the tail 
of a comet must be feebly attracted towards the 
body. The attraction lessens as the distance in- 
creases, not merely in a simple ratio, but accord- 
ing to the squares of the distance. Thus at the 
distances 2, 3, 4, — 10, the attraction, exerted by 
any body, is 4, 9, 16, — 100 times less than at the 
distance 1. 

We have seen that a comet, in consequence of 
the small quantity of matter it contains, exerts 
upon what is near it but a feeble attraction ; and 
upon particles far removed from its head the 
attraction must be hardly perceptible. Now have 
we not seen comets with very long tails ? In the 
comet of 1680, the extreme visible particles were, 
in a right line, about one hundred millions of miles 
from the nucleus. 

It will now be seen that a planet like the earth, 
the mass of which, for the most part, is much 
greater than that of a comet, must have the power 
of attracting and of drawing in and appropriating to 
itself the extreme particles in the tail of a comet, 
even when in its annual course it may be very dis- 
tant from it. 

The introduction of some new gaseous element 
into the terrestrial atmosphere might, as it was 
more or less abundant, occasion the death of all 
animals, or produce epidemics. Such, indeed, has 
been, according to various authors, the origin of 
most of those scourges which are mentioned in 
history. 

In a work on astronomy, published at Oxford, in 
1702, Gregory says, that among all nations, and in 



WONDERS OF THE HEAVENS 



209 



all ages, it has been observed that the appearance of 
a comet has always been followed by great calami- 
ties; and he adds, "it does not become philoso- 
phers lightly to set down these things as fables." 

Gregory has not confined himself within the strict 
limits of truth, when he gives as observations worthy 
of confidence the careless remarks of historians 
concerning a pretended influence of these bodies 
over the events of the world at the time of their 
appearance. 

An English physician, Mr. T. Forster, has lately 
treated particularly of this subject. According to 
him, " It is certain, that, ever since the Christian 
era, the most unhealthy periods are precisely those 
in which some great comet has appeared ; that the 
approach of these bodies to our earth has always 
been accompanied by earthquakes, eruptions of 
volcanoes, and atmospheric commotions; whereas 
no comet has ever been seen during the salubrious 
periods." 

The whole number of comets mentioned by histo- 
rians, reckoning from the beginning of the Christian 
era to the present time, is about five hundred. At 
the present time, when the heavens are examined 
attentively and skilfully, when comets that can be 
seen only by the aid of the telescope are no longer 
overlooked, the average number of these bodies is 
more than two for each year. If we agree with 
Forster that their influence begins before they are 
visible, and continues some time after, we shall 
never be without a comet to account for every 
phenomenon, misfortune, or epidemic, that can 
occur. 

Hot or cold seasons, tempests, hurricanes, earth- 
quakes, volcanic eruptions, violent hail-storms, 
great falls of snow, heavy rains, overflowings of 
rivers, droughts, famines, thick fogs, flies, grass- 
hoppers, plague, dysentery, contagious diseases 
among animals, &c., are all registered by Fors- 
ter as consequences of the appearance of some 
comet, whatever may be the continent, the king- 
dom, the town, or the village, so visited. By thus 
making out for each year a complete catalogue of 
all the miseries of this lower world, any one might 

foresee that a comet would never approach the 

27 



earth without finding a part of its inhabitants suf- 
fering under some calamity or other. 

By a strange accident, well worthy of remark, 
the year 1680, the year of the most brilliant of 
modern comets, the year of its passage so near the 
earth, is that which has furnished our author with 
the fewest phenomena. " A cold winter, followed 
by a hot and dry summer; meteors in Germany.'' As 
to maladies, we find no record whatever ! How 
then, with such a fact as this, can we attach any 
importance to the accidental coincidences noted in 
other parts of the table ? How are we to regard 
this celebrated comet of 1680, which, blowing now 
hot and now cold, increased the frosts of winter, 
and the heat of summer ? 

In 1665, the city of London was ravaged by the 
plague. If, with Forster, we attribute this to the 
remarkable comet which appeared the same year, 
in the month of April, how are we to explain why 
the same pestilence did not extend to America, to 
France, to Holland, or even to any of the other 
towns in England ? Until such a difficulty as this 
is done away, we shall expose ourselves to ridicule, 
and with good reason, if we attempt to make 
comets the messengers of evil. 

Let us now see which are the comets whose 
tails might have mingled with the earth's atmo- 
sphere, and then seek to discover whether, at the 
same time, there were manifested, in all parts of 
the earth at once, unusual phenomena ; though the 
extreme rarity of the matter which composes the 
tail would lead one to expect nothing but negative 
results. But when an author appends to the date 
of a comet, as to that of 1668, the remark that all 
the cats in Westphalia were sick; and to the date of a 
another, that a meteoric stone fell in Scotland into a 
high tower, and broke the wheels of a clock ; that, 
during the winter, wild pigeons appeared in large 
flocks in America, or that ^tna or Vesuvius threw 
out torrents of lava, " the gentle nymphs will 
smile." If, in thus registering contemporary events, 
he thinks he has established some new relations 
between them, he is as much mistaken as the 
woman, who, never having put her head out 
of her window without seeing coaches in the 



210 



WONDERS OF THE HEAVENS 



street, imagined herself to be the cause of their 
passing. 

When, in 1456, the splendid comet appeared 
which returned in November, 1835, Pope Calixtus 
was so terrified at it that he ordered public prayers 
to be offered up in all the churches ; and, in the 
middle of each day, the comet and the Turks were 
excommunicated. That no one need fail in this 
duty, he established the practice, which has been 
continued to this day, of ringing the church bells at 
noon. 

The fog of 1783 began nearly on the same day 
(the 18th of June) in places very distant from each 
other, as Paris, Avignon, Turin, Padua ; 

It extended from the northern coast of Africa to 
Sweden ; it was also observed in a great part of 
North America ; 

It lasted more than a month ; 

The air, at least that of the lower regions, did 
not appear to be its vehicle, because in some places 
it came on with a north wind, and in others with a 
south or east wind ; 

Travellers found it on the highest summits of 
the Alps ; 

The abundant rains that fell in June and July, 
and the highest winds, did not disperse it ; 

In Languedoc, its density was occasionally so 
great that the sun did not become visible in the 
morning, till it was twelve degrees above the 
horizon ; it was very red the rest of the day, and 
might be looked at with the naked eye. 

This fog or smoke, as some meteorologists have 
called it, had a disagreeable odor. 

The property by which it was particularly dis- 
tinguished from common fogs, was its being, by all 
accounts, very dry, whereas most fogs are moist. 
At Geneva, Senebier found that the hair hygrome- 
ter of Saussure, which in real fogs stands at 100°, 
ranged in the midst of this as low as 68°, 67°, 65°, 
and even 57°. 

Besides all this, there was one very remarkable 
quality in the fog or smoke of 1783 ; it appeared to 
possess a phosphoric property, a light of its own. 
We find, at least in the accounts of some observers, 
that it afforded, even at midnight, a light which 



they compare to that of the full moon, and which 
was sufficient to enable one to see objects distinctly 
at a distance of two hundred yards. To remove 
all doubts as to the source of this light, it is record- 
ed that at the time there was a new moon. 

Such is the state of the facts. Let us now see 
whether, in order to explain them, it will be neces- 
sary to admit that in 1783 the earth was immersed 
in the tail of a comet. 

The fog of 1783 was neither so constant nor so 
thick as to prevent the stars being seen every 
night in all the places where it occurred. Admit- 
ting therefore that the earth was in the tail of a 
comet, there is but one way of explaining why the 
head of that comet was never seen, and that is, by 
supposing that it rose and set almost at the same 
time with the sun ; that the superior light of that 
luminary rendered it invisible ; and that this con- 
junction of the sun and comet lasted more than a 
month. 

At a time when the proper motions of comets 
appeared subject to no rule, when every one dis- 
posed of them as he pleased, considering them as 
mere meteors, the supposition we have just made 
might be admitted ; but now that comets are known 
to all astronomers to be heavenly bodies, as obedi- 
ent as the planets to the laws of Kepler — now that 
the mutual dependence of distance and velocity is 
known — now that observation and theory combine 
to prove that all these bodies necessarily move in 
their orbits with a rapidity that increases as they 
approach the sun — it would be contrary to all estab- 
lished principles to admit that a comet, interposed 
between the sun and earth, could revolve about the 
sun in such a manner as to appear constantly near 
it for more than a month to a spectator on the 
earth ! It is in vain to attempt to explain the 
difficulty attending an exact conjunction by sup- 
posing the tail very large. If it were as large 
as that of 1744, the objection would remain in all 
its force. The dry fog of 1783, then, whatever 
may have been said of it, was not the tail of a 
comet. 

The remarkable fog of 1831, which excited the 
public mind in all quarters of the globe, resembled 



WONDERS OF THE HEAVENS 



211 



so much that of 1783 as to dispense with the 
necessity of proving that this also could not be 
attributed to the tail of a comet. 

But to what cause shall we attribute the fog of 
1783 ? We might suppose, with Franklin, that it 
was simply the result of the general diffusion of the 
thick columns of smoke emitted all summer by 
Mount Hecla, and carried about by the winds ; or 
we might avail ourselves of another suggestion of 
the illustrious American philosopher, for there is 
no reason against believing it, viz. that an immense 
fire-ball, in penetrating our atmosphere, was there 
but partially inflamed or ignited, and that torrents 
of smoke, occasioned by this imperfect combustion, 
were deposited in the higher regions of the air, and 
were afterwards carried into all the atmospheric 
strata by the action of common winds, and by the 
currents ascending and descending vertically, which 
exert so important an influence in meteorological 
phenomena. The passing of the earth through the 
tail of a comet, is an event that must happen 
several times in a century. If it did not occur in 
1819, and in 1823, it could only be on account of 
a purely accidental circumstance, that of the tail 
not being long enough to reach the earth ; for in 
each case it was for several hours directed exactly 
towards us. It is therefore important to prove 
that there is really no danger to be apprehended 
on this score, and that we even pass through these 
immense trains without being in the least aware of 
it. Now this may be considered as a fact clearly 
proved, if it be granted that the tail of a comet 
does not serve to explain all the circumstances 
attendant on the dry fogs of 1783 and 1831. 

Many authors have chosen to see some connec- 
tion between the extraordinary fog of 1831, and 
the entrance of the cholera morbus into Europe. 
This opinion reminds one of what an old English 
traveller says of the effects of a periodical wind on 
the west coast of the continent of Africa, which is 
called the Harmattan. 

A fog, of a particular kind, and thick enough to 
impede at noon all but the red rays of the sun, 
always presents itself where the Harmattan blows. 
The particles of which this fog is formed are de- 



posited on the grass, on the leaves of trees, and on 
the skin of the negroes, in such profusion as to pro- 
duce a white appearance. Of the nature of these 
particles we are ignorant. We only know that the 
wind carries them but a short distance from the 
shore. A league out at sea the fog is much lighter, 
and, at the distance of three leagues, it disappears 
entirely, although the Harmattan is still felt in all 
its force. 

The extreme dryness of the Harmattan is one of 
its most striking characteristics. When it lasts 
some time, the branches of orange and citron trees 
die ; the covers of books (even when these are 
shut up in tight trunks, and have an additional 
covering of linen) warp as if they had been before 
a glowing coal fire ; pannels of doors and furniture 
crack, and often break. The eflfects of this wind 
upon the human body are not less remarkable : the 
eyes, lips, and palate become dry and painful ; if 
the Harmattan lasts four or five days in succession, 
the skin of the hands and face come off". 

After what has been stated of the fatal effects of 
the Harmattan on vegetables, it may be thought 
that this wind must be very unhealthy, whereas quite 
the contrary is observed. Intermittent fevers are 
completely cured by the first breath of the Har- 
mattan. Patients reduced by the excessive bleed- 
ing practised in that country, recover their 
strength ; remittent and epidemic fevers also dis- 
appear, as if by enchantment. Such is the salutary 
influence of this wind, that, while it lasts, infection 
cannot be communicated even artificially. 

Whiston not only proposed to show in what 
manner a comet might have occasioned the deluge 
mentioned in the Scriptures, but he wished more- 
over to adapt his explanation to all the minute 
details of this great catastrophe as given in the 
book of Genesis, 

This flood took place in the year 2349 before the 
Christian era, according to the modern Hebrew 
text, or in the year 2926, according to the Samari- 
tan text, the Septuagint, and Josephus. Is there 
any reason to suppose that at either of these 
epochs there was a large comet present ? 

Among all the comets observed by modern 



212 



WONDERS OF THE HEAVENS 



astronomers, we may, without hesitation, consider 
that which appeared in 1680 as the first in point of 
brilliancy. 

Many historians mention a comet of great size, 
resembling the sun in brightness, and having an im- 
mense tail, which appeared in 1106. Going still 
further back, we find, in the year 531, a comet 
mentioned as very large and very alarming, called 
by the Byzantine writers lampadias, because it 
resembled a burning lamp. Every one has heard 
of the comet that appeared in the year of Caesar's 
death, during the games that Augustus was giving 
to the Romans. This must have been a very bril- 
liant comet, since its light began to be visible about 
five o'clock in the evening, or before sunset. -The 
date of this is the year 43 before our era. 

We have no exact observations of these bodies 
either in — 43, or in 531, or in 1106; we cannot 
calculate their parabolic orbits ; we are without the 
only criterion that would enable us to pronounce 
with certainty on the identity of two comets ; but 
let us observe that these, as well as the comet of 
1680, were peculiarly brilliant, and let us compare 
their dates. 

From 1106 to 1680 is a period of 574 years. 
531 " 1106 " 575 " 
" _^3 « 531 " 575 " 

As we have taken no note of months, or parts of 
years, these periods may be considered as equal 
among themselves, and it hence becomes probable 
that the comet which appeared at the time of 
Caesar's death, that of 531, of 1106, and of 1680, 
are periodical returns of the same body, which, 
after completing its revolution in about 575 years, 
becomes again visible from the earth. Now if we 
multiply this period of 575 years by four, we have 
2300, which, added to 43, the date of Caesar's 
comet, carries us back within six years of the time 
of the deluge, according to the modern Hebrew 
text. If we multiply by five, we have the date of 
it according to the Septuagint within eight years. 

If we consider the remarkable variations which 
the comet of 1759 exhibited in the duration of its 
revolution round the sun, we must allow that 
Whiston was justified in believing that the great 



comet of 1680, or Caesar's comet, was near the 
earth at the time of Noah's deluge, and had some 
effect in producing this great phenomenon. 

We shall not stop to examine particularly the 
series of transformations by which Whiston sup- 
poses the earth to have been changed from a comet 
to the globe we inhabit. It will suffice to say, that 
he believed the nucleus of the earth to be a hard 
and compact substance, and that it is the old 
nucleus of a comet ; that various kinds of matter, 
which, mixed together, formed the envelope, settled 
with more or less rapidity, according to their 
specific gravity ; that thus the solid nucleus was at 
first encompassed by a thick and heavy fluid ; that 
the earthy matter was then precipitated, forming 
upon the fluid a dense covering, a kind of crust, 
which may be compared to the shell of an egg ; 
that water came afterwards to cover this solid crust, 
filtering through the fissures and extending over 
the thick fluid; that finally the gaseous matter 
remained suspended, being gradually purified, and 
constituting at last our atmosphere. 

Thus, in this system, the great deep of the Bible 
is composed of a solid nucleus and two concentric 
orbs. The orb nearest the centre is formed of the 
heavy fluid which was first precipitated : the second 
is water. It is upon this latter fluid, then, that the 
exterior and solid crust of the earth rests. 

We must now examine how, according to this 
construction of the globe, against which modern 
geology offers many objections, Whiston has 
explained the two principal events of the deluge 
as described by Moses. 

" In the sixth hundredth year of Noah's life, in 
the second month, and the seventeenth day of the 
month, the same day we^'e all the fountains of the 
great deep broken up, and the flood-gates of heaven were 
opened." — Gen. vii. 11. 

At the time of the deluge, the comet of 1680, 
according to Whiston, was only seven or eight 
thousand miles from the earth. It must therefore 
have attracted the fluids of the great deep, as the 
moon attracts the waters of the ocean. Its action 
at this small distance must have produced an 
immense tide in the fluid beneath the earth. The 



WONDERS OF THE HEAVENS. 



213 



terrestrial crust, incapable of withstanding the 
impetuous flood, must have broken in many places. 
The waters were thus let loose, and allowed to 
spread themselves over the continents. Here the 
reader finds the breaking up of the fountains of the 
great deep. 

The ordinary rains of our globe, even if continued 
forty days, would have produced but a small effect. 
Taking for a day's rain all that falls in a year, 
the quantity that would fall in six weeks, far from 
covering the tops of the highest mountains, would 
hardly form a layer twenty-eight yards deep. We 
must therefore look further for the windows or flood- 
gates of heaven that were opened. Whiston has found 
them in the atmosphere, and in the tail of the 
comet. 

According to him, this atmosphere reached the 
earth towards the Gordsean mountains, (Ararat,) 
which mountains are supposed to have entirely 
intercepted the tail. The terrestrial atmosphere 
being thus charged with an immense quantity of 
aqueous particles, the consequence might be a rain 
of forty days, falling in such torrents as the ordinary 
state of the earth can give us no idea of 

Whiston, having occasion for an immense tide, 
in order to explain the phenomena of the great deep 
of the Bible, is not contented with making his 
comet pass very near the earth at the time of the 
deluge ; he has moreover given to it a mass six 
times as great as that of the moon. 

Such a supposition is wholly gratuitous ; and yet 
that is its least defect, for it does not, after all, 
explain the phenomena. The reason why the moon 
produces such a great effect upon the waters of the 
ocean is, because its daily angular motion is com- 
paratively small ; in the course of a few hours its 
distance from the earth scarcely varies at all; for 
some considerable time it continues vertical over 
the same points of our globe ; the waters attracted 
by it have always time enough to yield to its influ- 
ence before the moon removes to another region 
where its force would be differently directed. But 
this was not true of the comet of 1680. When 
near the earth, its angular motion, apparently 
through the constellations, must have been extremely 



rapid. In a few minutes it must have corresponded 
to a numerous series of points situated on meridians 
of the earth very distant from each other. As to 
its rectilinear distance from the earth, that might 
certainly have been very small, but only for a 
few short moments. These circumstances taken 
together are, it must be allowed, very unfavorable 
to the production of a great tide. 

In order to lessen these difficulties we have only 
to enlarge the comet, to make its mass not merely 
six times, but thirty or forty times, that of the 
moon. We cannot, however, be allowed this 
latitude with respect to the comet of 1680. In 
that year, on the 21st of November, it passed near 
the earth. It is proved that at the time of the 
deluge its distance was not less. Now, as in 1680 it 
produced neither floods from above, nor tides from 
below, nor any breaking up of the great deep — as, 
moreover, neither its tail nor its envelope inun- 
dated us — we may aflSrm with confidence that 
Whiston's theory is a mere romance, unless, giving 
up the comet of 1680, the same effects are ascribed 
to another body, of the same kind, but much larger. 

A few words, before quitting this subject, upon 
the consequences of a comet's striking the earth, so 
far as its rotary motion is concerned. 

The earth turns upon its axis in twenty-four 
hours from west to east. The circumference of 
the equator is a little more than twenty-four thou- 
sand miles. 

Twenty-four thousand miles, therefore, is the 
distance travelled by the equatorial regions, solid 
and fluid, every twenty-four hours, in consequence 
of the rotary motion of the globe. An observer 
who should be placed in space, and far enough 
removed from the earth and its atmosphere not to 
be carried round with it, would see every part of 
the equator pass before his eyes at the rate of about 
one thousand miles an hour, or seventeen in a 
minute. At the very poles, there is no motion. In 
the latitude of Brest, in France, the earth moves 
only at the rate of about ten miles in a minute. 

The waters of the ocean, though they participate 
in this rapid movement, do not overflow the land 
that surrounds them ; but this is because in every 






214 



WONDERS OF THE HEAVENS 



country the land has exactly the same velocity as 
the water. In all latitudes, the continents, and the 
seas that border on them, are, with regard to each 
other, in a state of relative rest. If this state of 
things were changed, if the water, in a given part 
of the globe, continued to move at its usual rate, 
whilst the land near it suddenly lost a part of its 
velocity, the ocean must overflow its boundaries. 

In order to have a clear idea of this subject, let us 
imagine, that, by an oblique stroke from a comet, all 
the solid parts of the earth were suddenly made to turn 
round the diameter, for instance,that passes through 
Brest. This town having become a pole, the whole 
peninsula of Brittany would be in a state of nearly 
absolute rest ; but the case would be very different 
with the ocean that washes it on the west, because, 
as we said just now in speaking of the progressive 
motion, the water is only laid upon the solid bed 
which contains it. The water would then be 
thrown in great masses on the shore, which would 
no longer flee before it with the former velocity of 
the parallel of Brest, namely, with a velocity of 
about ten miles a minute. 

Thus, through the agency of a comet, vast 
portions of a continent might be inundated, and 
high regions covered with water. But is it really in 
this way that the marine deposits, discovered on 
the tops of mountains, have been formed ? By no 
means. These beds are frequently horizontal, 
very extensive, deep, and regular. The shells are 
of various kinds, and it often happens that there 
are among them very small ones, in which the 
most delicate points and most fragile parts remain 
unbroken. All this is against their being carried 
there by violence. Every thing shows that the 
deposit was formed upon the spot. In what way, 
then, can we account for these marine beds, 
without supposing them to be formed by an irrup- 
tion of the ocean ? We must consider the moun- 
tains, and the more or less elevated lands which 
serve as their base, to have been gently heaved up 
from below, to have risen through the bosom of the 
waters, as mushrooms rise out of the earth. In 1694, 
Halley gave this hypothesis as a possible explanation 
I of the presence of marine productions on the tops 



1L_ 



and sides of mountains. This explanation was the 
true one ; and it is now almost universally admitted 
to be such. A com-et which should perceptibly 
change either the progressive or rotary motion of 
this globe, would, no doubt, occasion frightful con- 
vulsions in the crust of the earth; but these 
physical revolutions would differ, in a thousand 
ways, from those which are now the objects of study 
to geologists. 

All the regions of Europe contain, either in the 
bowels of their mountains, in caverns, or at mod- 
erate depths in certain kinds of earth, the bones of 
animals, such as the rhinoceros, elephant, &c., 
which are not now the inhabitants of such cold 
climates. We must then suppose, either that 
Europe, in the course of many ages, has become 
colder, or else that, during one of the violent 
deluges which this planet has experienced, currents, 
running from the south to the north, have carried 
with them the remains of numerous species of 
animals that were actually destroyed. 

Two very remarkable events have occurred to 
contradict the latter explanation, and to show its 
insufficiency. One is, the discovery, made in 
Siberia, in the year 1771, on the sandy shores of 
the Wilhoui, some feet below the surface, of a 
rhinoceros so perfectly preserved that it was covered 
with flesh and skin ; and the other is the later and 
still more curious discovery, made, in 1799, on the 
shores of the Frozen Ocean, near the mouth of the 
Lena, of an enormous elephant, enclosed in a block 
of ice, the flesh of which was so unchanged, that 
the Yakoutes of the neighborhood cut it up for their 
dogs to eat. In such a case as this, there could be 
no action of a current — no long transportation from 
the south to the north ; for if such large animals as 
these had not been frozen as soon as killed, their 
flesh would have become putrid. Are we therefore 
led to suppose that Siberia was once a warm country, 
since elephants and rhinoceroses lived in it ? and 
also to conclude that the same catastrophe which 
killed those animals, suddenly rendered that part 
of the globe the cold region we now find it ? 

In the present state of our knowledge, we can 
think of but one way in which the thermometrical 



WONDERS OF THE HEAVENS 



215 



character of a country could be materially and 
suddenly changed, and that is, by suddenly 
changing its latitude. Any other circumstances 
would make but a very slight difference. 

If deep snows cover Spitsbergen during half the 
year, it is only because it is situated very near one 
of the poles of rotation. Change the place of the 
pole ninety degrees — this archipelago Avould be at 
the equator, and its desert valleys, fertilized by the 
solar heat, would be clothed in the richest verdure. 
Imagine the earth's axis to be somewhere in Peru 
or Brazil, without the inclination of the equator to 
the ecliptic being changed, and there would soon 
be icebergs floating in the ports of Callao and 
Rio Janeiro. The thousand beautiful plants Avhich 
now enrich and embellish those countries, would 
perish under deep snows, and be replaced by 
lichens. We need not hesitate to say, that if any 
other tropical region became suddenly the pole of 
the earth, it would freeze there in less than twenty- 
four hours. 

The problem to which the elephant of Siberia 
has given rise, leads, then, at last, to this question : 
Has the earth's axis of rotation ever suddenly 
changed its direction? 

Such a change, particularly if very sudden, could 
not be produced by the forces usually acting upon 
our globe; but if the earth should be violently 
struck by a foreign body, a change of place in the 
axis round which it turns would be the almost 
necessary consequence. Almost^ because there are 
directions in which a blow, however hard, would 
not alter the original position of the axis. 

Comets are evidently the only foreign bodies in 
our system that could possibly strike the earth. 
The Lena elephant, and the Wilhoui rhinoceros 
seem then to prove, however strange such a catas- 
trophe may seem, that in the lapse of ages a ren- 
contre of that nature has taken place. This proof 
would even be indubitable, if it were well ascertained 
that elephants have never been able to live in such 
a climate as that of Siberia. Now some doubts are 
entertained on this subject, of which the reader may 
judge from the following facts. 

In form and dimensions the elephant of the 



Frozen Ocean bore a great resemblance to those 
that inhabit Africa and Asia, His tusks were ten 
feet long ; his head weighed four hundred and fifty 
pounds; but his skin exhibited a very marked 
peculiarity, and one well worthy of notice — it was 
covered with long black hair, and a reddish, woolly 
coat. The white bears, in devouring the flesh, had 
trampled into the wet soil more than thirty pounds 
of this hairy coat, which were taken up by Mr. 
Adams. The neck was also furnished with a long 
mane. 

This double coat of the polar elephants, and the 
stiff hair, three or four inches long, which covered 
the skin of the Wilhoui rhinoceros, were too well 
adapted to the severity of a Siberian climate for us 
to entertain a doubt as to these animals being able 
to live in very cold climates, though, without such 
warm covering, those of their race now living could 
not endure them. Moreover, Humboldt became 
acquainted, in his travels, with an important fact, 
very much to our purpose, and likely to throw new 
light upon the subject. He ascertained that the 
royal tiger of India, which we are accustomed to 
call a tropical animal, lives in Asia in very high 
latitudes, and that in summer it makes excursions 
to the western side of the Altai mountains, near 
Barnoul, where several have been killed of an 
enormous size. It appears, then, that elephants 
with thick coats must have been formerly able to 
travel, during summer, as far as Siberia. Once 
there, any common accident, a mere slide of earth, 
would be su^Iicient to account for their bodies being 
found in frozen beds, capable of preserving them 
from decomposition. The observations of Humboldt 
prove, that, in the steppes beyond the sixty-second 
degree of latitude, the earth, at a depth of fourteen 
or fifteen feet, is always frozen. 

While it is thus shown that we can satisfactorily 
account for fossil elephants being found in Siberia, 
without admitting that there has been a sudden 
change of climate, we may here also assert that 
nothing has yet been brought forward to prove that 
a comet has ever had any agency in the great 
physical revolutions on our globe, of which traces 
are everywhere to be seen. 



216 



WONDERS OF THE HEAVENS 



As soon as the northern regions of America were 
discovered, navigators remarked that they were 
much colder than the same parallels in Europe. 
This fact, for which the astronomical theory of 
climates does not satisfactorily account, has exer- 
cised the ingenuity of many philosophers, and, 
among the rest, of Halley. According to that 
learned and celebrated man, a comet formerly 
struck the earth obliquely, and changed the position 
of its axis of rotation, in consequence of which the 
north pole, which was once very near Hudson's 
Bay, was carried further eastward. The country 
which it left had been so long and so deeply frozen, 
that the effects of this once polar cold are still 
experienced, and a long series of years must elapse 
before the northern parts of the new world can 
receive, by the action of the sun's rays, that climate 
which its geographical position indicates. 

This might have appeared to be a plausible 
hypothesis in the time of Halley. But now that 
the meteorological fact w^hich it was meant to 
explain is understood in all its details, it is found 
to be insufficient and useless, and even opposed to 
the results of observation. 

It is true that, in the same latitudes, it is much 
colder in the United States than in Europe; but 
this difference disappears almost entirely when the 
points of comparison in America are taken from the 
western side of that continent, that is, on the shores 
of the Pacific Ocean. Thus, according to Halley's 
hypothesis, the old north pole has modified only 
the temperature on the eastern side of the con- 
tinent: this pole must then have been situated 
originally in that part, or on the meridians near it. 
But then what is to be said as to the cause of the 
excessive cold on the coast of Asia, which, in similar 
latitudes, is not less severe than it is on the Atlantic 
coast of North America? It cannot be denied 
that Halley was acquainted with but a small part 
of the interesting phenomena that belong to the 
subject of climate. He was not aware, that, in the 
old world, as well as in the new, the eastern coast 
is remarkable for its low temperature ; that the 
lines of equal temperature, called now isothermal 
lines by Humboldt, differ greatly from terrestrial 



parallels; that they incline towards the equator 
according as, leaving the western coast, we ap- 
proach the interior of continents. Halley's hypo- 
thesis is wholly unsatisfactory, and there are no 
meteorological phenomena to prove that the axis of 
the earth has ever undergone any change by the 
shock of a comet. 

Russia and Persia present us with a geographical 
phenomenon truly extraordinary. There is in these 
countries a vast region, covered with populous 
towns, great commercial establishments, and fertile 
lands, which is nevertheless much below the level of 
the ocean. According to Humboldt, the extent of 
this low region cannot be less than one hundred 
thousand square miles. That no one may imagine 
the depression to be slight, or that it is over- 
estimated on account of errors liable to be committed 
in ascertaining the level of very large tracts, we 
will observe that the level of the Caspian Sea, and 
consequently that of the city of Astracan, is more 
than three hundred feet below the level of the 
Black Sea, or of the ocean. Even in the heart of 
Russia, the course of the Wolga, and the countries 
through which it flows, are depressed one hundred 
and fifty feet. 

This enormous sinking of a whole country, a 
phenomenon of which the globe does not offer 
another example, being very difficult to explain by 
the operation of known causes, has led persons, in 
despair of all other agency, to attribute it to the 
action of a comet. 

In ricochet firing, it is evident that the spot struck 
by the ball is somewhat depressed. Thus, accord- 
ing to some, the Caspian Sea and the surrounding 
country has been indented by the stroke of an 
immense ball, that is, of a comet. 

In the present state of geological science, this 
idea of Halley's cannot be favorably received. No 
one doubts now that isolated peaks, as well as the 
longest and highest ranges of mountains, have been 
gradually heaved up from the bosom of the earth. 
Now the very idea of a rise necessarily implies a 
void in some neighboring part, and the possibility of 
an ulterior depression. 

In looking at a map of Asia, it will be easily 



WONDERS OF THE HEAVENS. 



217 



seen that no other part of the world contains so 
much high land. Around the Caspian Sea are the 
large elevated regions of Iran and of central Asia, 
those of Himalaya, of Kuen-Lun, of Thian-Chan, 
the mountains of Armenia, those of Erzerum, and 
the range of Caucasus. Now, without calling in 
the aid of a comet, may we not suppose, as 
Humboldt does, in his "Asiatic Fragments," that 
the uplifting of so many enormous masses must be 
attended with a perceptible depression in the 
intermediate places? This solution of one of the 
most curious problems in physical geography is less 
liable to objection on account of the actual state of 
the ground in the region to which it belongs, 
which has not yet become stable. The bottom of 
the Caspian Sea, for instance, is occasionally raised 
and depressed. 

The Arcadians thought themselves of older date 
than the moon. They maintained that their ances- 
tors had inhabited this planet before it had any 
satellite. Struck with this singular opinion, some 
philosophers have imagined that the moon was 
formerly a comet, which, in performing its elliptical 
course round the sun, came into the neighborhood 
of the earth, and was drawn in to revolve around it. 

Such a change of orbit is possible ; but it evident- 
ly could not have taken place if the comet's peri- 
helion distance had been great. The comet must, 
therefore, have passed very near the sun, and have 
experienced an intense heat, capable of dissipating 
every trace of humidity. The almost entire absence 
of an atmosphere round the moon, the scorched 



appearance of its vast mountains and deep valleys, 
and the few plains that are seen, have been cited as 
proofs that this luminary was once a comet. 

This reasoning is founded upon the strangest 
confusion of language. The moon has, indeed, a 
scorched appearance, if by that is meant that all 
parts of its surface show traces of former volcanic 
eruptions ; but nothing in its aspect indicates, or can 
indicate at the present day, what temperature the 
moon has heretofore been subjected to by the action 
of the solar rays. These two phenomena have no 
connection with each other. The volcanoes of 
Iceland, of Mayen's Island, and of Kamtschatka, 
show every year that the frosts at the surface of 
polar regions have no effect upon the subterraneous 
matter, the chemical action of which produces 
eruptions. 

In all the multitude of bodies, of various forms 
and degrees of brightness, which the firmament 
displays, comets are the only ones which are evi- 
dently and sensibly surrounded with a gaseous 
envelope, a real atmosphere. We do not deny 
that this atmosphere has been formed by the evap- 
oration of matter which originally existed in the 
nucleus; but it is always found to accompany a 
comet, and there would be no reason for its being 
separated from it, whatever derangement the comet 
might experience in the form and original position 
of its orbit from an accidental attraction. Thus 
the small extent of atmosphere around the moon, 
is rather against than for the opinion that it was 
once a comet. 



CHAPTER VII. 



Reflections on the system — Proofs from analogy that the planets are 
inhabited — Their magnitude — Their rotation — Their revolution 
round the sun — They have moons — Mountains and valleys — Clouds 
and snow — Our globe a small part of the universe — No limits to 
future discoveries — Rapid motion of the planets — Infinite power 
requisite to give them this motion — Immense spaces around the 
heavenly bodies^Their mutual influences — Astronomy an aid to 
religion. 

28 



Such is a general outline of the leading facts con- 
nected with that system of which we form a part. 
Though the energies of Divine Power had never 
been exerted beyond the limits of this system, it 
would remain an eternal monument of the wisdom 
and omnipotence of its Author. Independent of 



218 



WONDERS OF THE HEAVENS. 



the sun, which is like a vast universe in itself, and 
of the numerous comets which are continually 
traversing its distant regions, it contains a mass of 
material existence, arranged in the most beautiful 
order, two thousand five hundred times larger than 
our globe. 

Such a glorious system must have been brought 
into existence to subserve purposes worthy of the 
infinite wisdom and benevolence of the Creator. 
To suppose that the distant globes of which it is 
composed, with their magnificent apparatus of rings 
and moons, were created merely for the purpose of 
affording a few astronomers, in these latter times, 
a peep at them through their glasses, would be in- 
consistent with every principle of reason, and would 
be charging Him who is the source of wisdom with 
conduct which we would pronounce to be folly in 
the sons of men. 

What a magnificent idea of the Creator and his 
works is presented to the imagination even by the 
bodies themselves ! The sun, a stupendous lumi- 
nous globe, is placed at the centre of the system, 
around whose orb the planets, satellites, and comets 
perform their revolutions with an order and regu- 
larity that must fill our minds with the most exalted 
conceptions of their divine original. Who can con- 
template the magnitudes and distances of these vast 
bodies, and not be struck with the grandeur of the 
scene, and the power of omnipotence ? What 
wonder, then, that the ancients should imagine that 
these spheres made a divine melody as they rolled 
on in their orbits, or even that some should be 
found enthusiastic enough to fancy that they some- 
times heard this "music of the spheres ? " 

Shall we conclude that all these glorious orbs 
are desolate and forsaken ? Shall we suppose 
them monuments of omnipotence only, and not of 
infinite goodness also ? 

Let us look around us, and reflect upon the 
evidence afforded by nature and analogy on this 
subject, and, other guides failing, let us follow these 
to whatever conclusions they may lead. 

The world in which we live is a round ball, of a 
determined magnitude, and occupies its own place 
in the firmament. But when we explore the un- 



limited tracts of that space which is everywhere 
around us, we meet with other balls of equal or 
superior magnitude, and from which our earth 
would either be invisible, or appear as small as any 
of those twinkling stars which are seen on the 
canopy of heaven. Why then suppose that this 
little spot — little at least in the immensity which 
surrounds it — should be the exclusive abode of life 
and intelligence ? What reason to think that 
those mightier globes which roll in other parts of 
creation, and which we have discovered to be 
worlds in magnitude, are not also worlds in use and 
in dignity ? Why should we think that the great 
Architect of nature, supreme in wisdom as he is in 
power, would call these stately mansions into 
existence, and leave them unoccupied ? When we 
cast our eye over the broad sea, and look at the 
country on the other side, we see nothing but the 
blue land stretching obscurely over the distant 
horizon. We are too far away to perceive the 
richness of its scenery, or to hear the sound of its 
population. Why not extend this principle to the 
still more distant parts of the universe ? What 
though, from this remote point of observation, we 
can see nothing but the naked roundness of yon 
planetary orbs? Are we therefore to say that 
they are so many vast and unpeopled solitudes ; 
that desolation reigns in every part of the universe 
but ours ; that the whole energy of the divine attri- 
butes is expended on one insignificant corner of 
these mighty works ; and that to this earth alone 
belongs the bloom of vegetation, or the blessedness 
of life, or the dignity of rational and immortal 
existence? 

But this is not all. We have something more 
than the mere magnitude of the planets to allege 
in favor of the idea that they are inhabited. We 
know that this earth turns round upon itself; and 
we observe that all those celestial bodies which 
are accessible to such an observation have the 
same movement. We know that the earth performs 
a yearly revolution round the sun; and we can 
detect in all the planets which compose our system 
a revolution of the same kind, and under the same 
circumstances. They have the same succession of 



WONDERS OF THE HEAVENS. 



219 



day and night. They have the same agreeable 
vicissitude of the seasons. To them, light and 
darkness succeed each other; and the gaiety of 
summer is followed by the dreariness of vi^inter. 
To each of them the heavens present as varied and 
magnificent a spectacle ; and this earth, the encom- 
passing of which would require the labor of years 
from one of its inhabitants, is but one of the lesser 
lights which sparkle in their firmament. To them, 
as well as to us, has God divided the light from the 
darkness. 

In all the greater arrangements of divine wisdom, 
we can see that God has done the same things for 
the accommodation of the planets that he has done 
for the earth which we inhabit. And shall we say 
that the resemblance stops here, because we are 
not in a situation to observe it? Shall we say 
that this scene of magnificence has been called into 
being merely for the amusement of a few astron- 
omers ? Shall we measure the counsels of heaven 
by the narrow impotence of the human faculties? 
or conceive that silence and solitude reign through- 
out the mighty empire of nature; that the greater 
part of creation is an empty parade ; and that not 
a worshipper of the Divinity is to be found through 
the wide extent of yon vast and immeasurable 
regions ? 

It lends a delightful confirmation to the argu- 
ment, when, from the growing perfection of our 
instruments, we can discover a new point of resem- 
blance between our earth and the other bodies of 
the planetary system. It is now ascertained, not 
merely that all of them have their day and night, 
and that all of them have their vicissitudes of 
seasons, and that some of them have their moons 
to rule their night and alleviate the darkness of it. 
We can see of one, that its surface rises into ine- 
qualities, that it swells into mountains and stretches 
into valleys ; of another, that it is surrounded by 
an atmosphere which may support the respiration 
of animals ; of a third, that clouds are formed and 
suspended over it, which may minister to it all the 
bloom and luxuriance of vegetation ; and of a fourth, 
that a white color spreads over its northern regions, 
as its winter advances, and that on the approach of 



summer this whiteness is dissipated — giving room 
to suppose that the element of water abounds in 
it, that it rises by evaporation into its atmosphere, 
that it freezes upon the application of cold, that it 
is precipitated in the form of snow, that it covers 
the ground with a fleecy mantle which melts away 
from the heat of a more vertical sun ; and that 
other worlds bear a resemblance to our own in 
the same yearly round of beneficent and interesting 
changes. 

Who shall assign a limit to the discoveries of 
future ages? Who can prescribe to science her 
boundaries, or restrain the active and insatiable 
curiosity of man within the circle of his present 
acquirements? We may guess with plausibility 
what we cannot anticipate with confidence. The 
day may yet be coming when our instruments of 
observation shall be inconceivably more powerful. 
They may ascertain still more decisive points of 
resemblance. They may resolve the same ques- 
tion by the evidence of sense which is now so 
abundantly convincing by the evidence of analogy. 
They may lay open to us the unquestionable ves- 
tiges of art, and industry, and intelligence. We 
may see summer throwing its green mantle over 
those mighty tracts, and we may see them left 
naked and colorless after the flush of vegetation 
has disappeared. In the progress of years, or of 
centuries, we may trace the hand of cultivation 
spreading a new aspect over some portion of a 
planetary surface. Perhaps some large city, the 
metropolis of a mighty empire, may expand into 
a visible spot by the powers of some future tele- 
scope. 

The discoveries of science widen the empire of 
creation far beyond the limits which were formerly 
assigned to it. They give us to see that the sun, 
throned in the centre of his planetary system, 
gives light, and warmth, and the vicissitude of 
seasons, to an extent of surface several hundreds 
of times greater than that of the earth which w^e 
inhabit. They lay open to us a number of worlds, 
rolling in their respective circles around this vast 
luminary, and prove that the ball which we tread 
upon, with all its mighty burden of oceans and con- 



220 



WONDERS OF THE HEAVENS 



tinents, instead of being distinguished from the 
others, is among the least of them, and, from some 
of the more distant planets, would not occupy a 
visible point in the concave of their firmament. 
They let us know, that, though this mighty earth, 
with all its myriads of people, were to sink into 
annihilation, there are some worlds where an event 
so awful to us would be unnoticed and unknown, 
and others where it would be nothing more than 
the disappearance of a little star which had ceased 
from its twinkling. We should learn not to look 
on our earth as the universe of God, but as a small 
portion of it ; as only one of the many mansions 
which the Supreme Being has created for the 
accommodation of his worshippers ; only one of the 
many worlds rolling in that flood of light which the 
sun pours around him to the outer limits of the 
planetary system. 

Since it appears, so far as our observation 
extends, that matter exists solely for the sake of 
sensitive and intelligent beings, and that the Crea- 
tor made nothing in vain, it is a conclusion, to which 
we are necessarily led, that the planetary globes 
are inhabited by various orders of intellectual 
beings, who participate in the bounty, and celebrate 
the glory, of their Creator. 

Here, then, with reverence, let us pause and 
wonder! Over all this vast assemblage of material 
existence God presides. Amidst the diversified 
objects and intelligences it contains, he is eternally 
and essentially present. By his unerring wisdom 
all its complicated movements are directed. By 
his almighty fiat it emerged from nothing into 
existence, and is continually supported from age to 
age. "He spake and it was done; he com- 
manded and IT STOOD FAST."'' " By the word of 
the Lord were the heavens made, and all the host 
of them by the spirit of his mouth." What an 
astonishing display of divine power is here exhibited 
to our view! How far transcending all finite com- 
prehension must be the energies of Him who only 
"spake, and it was done;" who only gave the 
command, and this mighty system of the universe, 
with all its magnificence, started into being! The 
infinite ease with which this vast fabric was reared, 



leads us irresistibly to conclude that there are 
powers and energies in the divine mind which 
have never yet been exerted, and which may unfold 
themselves to intelligent beings, in the production 
of still more astonishing and magnificent effects, 
during an endless succession of existence. 

We can acquire accurate ideas of the relative 
velocities of moving bodies only by comparing the 
motions with which we are familiar, with one 
.another, and with those which lie beyond the 
general range of our minute inspection. We can 
acquire a pretty accurate conception of the velocity 
of a ship impelled by the wind — of a steam-car — 
of a race horse — of a bird darting through the air — 
of an arrow flying from a bow — and of the clouds 
when impelled by a stormy wind. The velocity of 
a ship is from eight to twelve miles an hour — of a 
race horse, from twenty to thirty miles — of a bird, 
say from fifty to sixty miles — and of the clouds, in a 
violent hurricane, from eighty to one hundred miles 
an hour. The motion of a ball from a loaded 
cannon is incomparably swifter than any of the 
motions now stated ; but of the velocity of such a 
body we have a less accurate idea, because, its 
rapidity being so great, we cannot trace it distinctly 
by the eye, through its whole range, from the mouth 
of the cannon to the object against which it is 
impelled. By experiments, it has been found that 
its rate of motion is from four hundred and eighty 
to eight hundred miles in an hour ; but it is retarded 
every moment by the resistance of the air and the 
attraction of the earth. This velocity, however, 
great as it is, bears no sensible proportion to the 
rate of motion which is found among the celestial 
orbs. That such enormous masses of matter should 
move at all is wonderful; but when we consider 
the amazing velocity with which they are impelled, 
we are lost in astonishment. The planet Jupiter, 
in describing its circuit round the sun, moves at 
the rate of twenty-nine thousand miles an hour. 
The planet Venus, one of the nearest and most 
brilliant of the celestial bodies, and about the same 
size as the earth, is found to move through the 
spaces of the firmament at the rate of seventy-six 
thousand miles an hour; and the planet Mercury 



WONDERS OF THE HEAVENS 



221 



with a velocity no less than one hundred and fifty 
thousand miles an hour, or one thousand seven hun- 
dred and fifty miles in a minute — a motion two 
hundred times swifter than that of a cannon ball. 

These velocities will appear still more astonish- 
ing, if we consider the magnitude of the .bodies 
which are thus impelled, and the immense forces 
which are requisite to carry them along in their 
courses. However rapidly a ball flies from the 
mouth of a cannon, it is the flight of a body only a 
^ew inches in diameter ; but one of the bodies, whose 
motion has been just now stated, is eighty-six thou- 
sand miles in diameter, and would comprehend 
within its vast circumference more than a thousand 
globes as large as the earth. Could we contem- 
plate such motions, from a fixed point, at the 
distance of only a few hundreds of miles from the 
bodies thus impelled, it would raise our admiration 
to its highest pitch, it Avould overwhelm all our 
faculties, and, in our present state, would produce 
an impression of awe, and even of terror, beyond 
the power of language to express. The earth con- 
tains a mass of matter equal in weight to at least 
2,200,000,000,000,000,000,000 tons, supposing its 
mean density to be only about two and a half times 
greater than water. To move this ponderous mass 
a single inch beyond its position, were it fixed in a 
quiescent state, would require a mechanical force 
almost beyond the power of numbers to express. 
The physical force of all the myriads of intelligences 
within the bounds of the planetary system, though 
their powers were far superior to those of man, 
would be altogether inadequate to the production of 
such a motion. How much more must be the force 
requisite to impel it with a velocity one hundred 
and forty times swifter than a cannon ball, or sixty- 
eight thousand miles an hour, the actual rate of its 
motion in its course round the sun ! But whatever 
degree of mechanical power would be requisite to 
produce such a stupendous effect, it would require 
a force one hundred and fifty times greater to impel 
the planet Jupiter in its actual course through the 
heavens! Even the planet Saturn, one of the 
slowest-moving bodies of our system, a globe ten 
hundred times larger than the earth, is impelled 



through the regions of space at the rate of twenty- 
two thousand miles an hour, carrying along with 
it two rings, and seven moons larger than ours, 
through its whole course round the central lumi- 
nary. Were we placed within a thousand miles of 
this stupendous globe, where its hemisphere, 
encompassed by its magnificent rings, would fill the 
whole extent of our vision, the view of such a 
glorious object, flying with such amazing velocity 
before us, would infinitely exceed every idea of 
grandeur we can derive from terrestrial scenes, and 
overwhelm our powers with astonishment and awe. 
The ideas of strength and power implied in the 
impulsion of such enormous masses of matter 
through the illimitable tracts of space, are forced 
upon the mind with irresistible energy, far surpass- 
ing what any abstract propositions or reasonings 
can convey. 

If we consider the immense number of bodies thus 
impelled through the vast spaces of the universe — 
the rapidity with which the comets, when near the 
sun, are carried through the regions they traverse ; 
if we consider the high probability, if not absolute 
certainty, that the sun, with all his attendant 
planets and comets, is impelled with a still greater 
degree of velocity towards some distant region of 
space, or around some wide circumference — that 
all the thousands of systems of that nebulae to 
which the sun belongs are moving in a similar 
manner — that all the nebulae in the heavens are 
moving around some magnificent central body — in 
short, that all the suns and worlds in the universe 
are in rapid and perpetual motion, as constituent 
portions of one grand and boundless empire, of 
which Jehovah is the sovereign; and if we con- 
sider, still farther, that all these mighty movements 
have been going on, without intermission, during 
the course of many centuries, and some of them, 
perhaps, for myriads of ages before the foundations 
of our world were laid; — it is impossible for the 
human mind to form any adequate idea of the 
stupendous forces which are in incessant operation 
throughout the unlimited empire of the Almighty. 
To estimate such mechanical force, even in a single 
instance, completely baflles the mathematician's 



222 



WONDERS OF THE HEAVENS 



skill, and sets the power of numbers at defiance. 
"Language," and figures, and comparisons, are 
"lost in wonders so sublime," and the mind, over- 
powered with such reflections, is irresistibly led 
upwards to search for the cause in that Omnipo- 
tent Being who upholds the pillars of the universe, 
the thunder of whose power none can compre- 
hend. While contemplating such august objects, 
how emphatic and impressive appears the language 
of the sacred oracles: "Canst thou by searching 
find out God? Canst thou find out the Almighty 
to perfection?" 

Again, the immense spaces which surround the 
heavenly bodies, and in which they perform their 
revolutions, tend to expand our conceptions on this 
subject, and to illustrate the magnificence of the 
divine operations. In whatever point of view we 
contemplate the scenery of the heavens, an idea of 
grandeur irresistibly bursts upon the mind ; and, if 
empty space can, in any sense, be considered as an 
object of sublimity, nothing can fill the mind with 
a grander idea of magnitude and extension than 
the amplitude of the scale on which planetary 
systems are constructed. Around the body of the 
sun there is allotted a cubical space three thousand 
and eight hundred millions of miles in diameter, in 
which eleven planetary globes revolve, every one 
being separated from another by intervals of many 
millions of miles. The space which surrounds the 
utmost limits of our system, extending in every 
direction to the nearest fixed stars, is, at least, 
40,000,000,000,000 miles in diameter; and it is 
highly probable that every star is surrounded by a 
space of equal, or even of greater, extent. A body 
impelled with the greatest velocity which art can 
produce, (a cannon ball, for instance,) would require 
twenty years to pass through the space that inter- 
venes between the earth and the sun, and four 
millions seven hundred thousand years ere it could 
reach the nearest star. Though the stars seem to 
be crowded together in clusters, and some of them 
almost to touch one another, yet the distance 
between any two stars which seem to make the 
nearest approach, is such as neither words can 
express, nor imagination fathom. These immense 



spaces are as unfathomable on the one hand, as the 
magnitude of the bodies which move in them, and 
their prodigious velocities, are incomprehensible on 
the other ; and they form a part of those magnificent 
proportions according to which the fabric of univer- 
sal nature was arranged, all corresponding to the 
majesty of that infinite and incomprehensible Being 
"who measures the ocean in the hollow of his 
hand, and meteth out the heavens with a span." 
How wonderful that bodies at such prodigious dis- 
tances should exert a mutual influence on one 
another! that the sun, at the distance of ninety-five 
millions of miles, should raise the vapors, move the 
ocean, direct the course of the winds, fructify the 
earth, and distribute light and heat and color 
through every region of the globe ; yea, that his 
attractive influence and fructifying energy should 
extend even to the planet Herschel, at the distance 
of nineteen hundred millions of miles! So that, in 
every point of viev/ in which the universe is con- 
templated, we perceive the same grand scale of 
operation by which the Almighty has arranged the 
provinces of his universal kingdom. 

We would now ask, in the name of all that is 
sacred, whether such magnificent manifestations of 
Deity ought to be considered as irrelevant to reli- 
gion? If religion consists in the intellectual appre- 
hension of the perfections of God, and in the moral 
effects produced by such an apprehension — if all 
the rays of glory emitted by the luminaries of hea- 
ven are only so many reflections of the grandeur 
of Him who dwells in light unapproachable — if they 
have a tendency to assist the mind in forming its 
conceptions of that ineffable Being whose uncreated 
glory cannot be directly contemplated — and if they 
are calculated to produce a sublime and awful im- 
pression on all created intelligences, — shall we rest 
contented with a less glorious idea of God than his 
works are calculated to afford ? Shall we disregard 
the works of the Lord, and contemn "the opera- 
tions of his hands? " If, at the command of God, 
we lift up our eyes to the "firmament of his power," 
surely we ought to do it, not with a brute "uncon- 
scious gaze," not with the vacant stare of a savage, 
not as if we were still enveloped with the mists and 



WONDERS OF THE HEAVENS 



223 



prejudices of the dark ages, but as surrounded by 
that blaze of light which modern science has thrown 
upon the scenery of the sky, in order that we may 
contemplate with fixed attention all that enlight- 
ened reason, aided by the nicest observations, has 
ascertained respecting the magnificence of the 
celestial orbs. To overlook the sublime dis- 
coveries of modern times, to despise them, or to 
call in question their reality, because they bring to 
our ears such astonishing reports of the "eternal 
power" and majesty of Jehovah, is to act as if Ave 
were afraid lest the Deity should be represented as 
more grand and magnificent than he really is, and 
as if we would be better pleased to pay him a less 
share of homage and adoration than is due to his 
name. 

Any person of common understanding may be 
made to comprehend the leading ideas of extended 
space, magnitude, and motion, which have been 
stated above, provided the descriptions be suffi- 
ciently simple, clear, and well-defined; and should 
they be at a loss to comprehend the principles on 
which the conclusions rest, or the mode by which 
the magnificence of the works of God has been 
ascertained, an occasional reference to such topics 
would excite them to inquiry and investigation, and 
to the exercise of their powers of observation and 
reasoning on such subjects, which are too fre- 
quently directed to far less important objects. The 
following illustration, however, stands clear of every 
objection of this kind, and is level to the compre- 
hension of every man of common sense. Either 
the earth moves round its axis once in twenty-four 
hours, or the sun, moon, planets, comets, stars, 
and the whole frame of the universe, move around 
the earth in the same time. There is no alterna- 
tive, or third opinion, that can be formed on this 
point. If the earth revolve on its axis every 
twenty-four hours to produce the alternate succes- 
sion of day and night, the portions of its surface 
about the equator must move at the rate of more 
than a thousand miles an hour, since the earth is 
more than twenty-four thousand miles in circum- 
ference. This view of the fact, when attentively 
considered, furnishes a most sublime and astonishing 



idea. That a globe of such vast dimensions, with 
all its load of mountains, continents, and oceans, 
comprising within its circumference a mass of two 
hundred and sixty-four thousand millions of cubical 
miles, should whirl round with so amazing a velocity, 
gives us a most august and impressive conception 
of the greatness of that Power which first set it in 
motion, and continues the rapid whirl from age to 
age ! Though the huge masses of the Andes were 
in a moment detached from their foundations, 
carried aloft through the regions of the air, and 
tossed into the Pacific, it would convey no idea of a 
force equal to that which is every moment "exerted 
if the earth revolve on its axis. But should the 
motion of our earth be called in question, or denied, 
the idea of force, or power, will be indefinitely 
increased. For, in this case, it must necessarily 
be admitted that the heavens, with all the innu- 
merable host of stars, have a diurnal motion around 
the globe, which motion must be inconceivably 
more rapid than that of the earth, on the supposi- 
tion of its motion. For, in proportion as the 
celestial bodies are distant from the earth, in the 
same proportion would be the rapidity of their 
movements. The sun, on this supposition, would 
move at the rate of four hundred and fourteen thou- 
sand miles in a minute ; the nearest stars, at the rate 
of fourteen hundred millions of miles in a second; 
and the most distant luminaries, with a degree of 
swiftness which no numbers could express. Such 
velocities, too, would be the rate of motion, not 
merely of a single globe like the earth, but of all 
the ten thousand times ten thousand spacious globes 
that exist within the boundaries of creation. This 
view conveys an idea of power still more august 
and overwhelming than any of the views already 
stated, and we dare not presume to assert that 
such a degree of physical force is beyond the limits 
of infinite perfection. But on the supposition it 
existed, it would confound all our ideas of the 
wisdom and intelligence of the Divine mind, and 
would appear altogether inconsistent with the 
character which the scripture gives us of the Deity 
as " the only wise God ;" for, it would exhibit a 
stupendous system of means altogether dispropor- 



224 



WONDERS OF THE HEAVENS 



tioned to the end intended — namely, to produce 
the alternate succession of day and night to the 
inhabitants of our globe, which is more beautifully 
and harmoniously effected by a simple rotation on 
its axis, as is the case with the other globes which 
compose the planetary system. Such considera- 
tions, however, show us, that, on whatever hypo- 
thesis, whether on the vulgar or the scientific, or 
in whatever other point of view, the frame of nature 



may be contemplated, the mind is irresistibly 
impressed with ideas of power, grandeur, and mag- 
nificence. And, therefore, when an inquiring mind 
is directed to contemplate the works of God, on 
any hypothesis it may choose, it has a tendency to 
arouse reflection, and to stimulate the exercise 
of the moral and intellectual faculties, upon 
objects that are worthy of the dignity of immortal 
minds. 



CHAPTER VIII. 



SECTION I. 

Eclipses — All opaque bodies cast shadows — The moon visible during 
total eclipses — Explanation of this phenomenon — Lunar eclipses 
universal — The shadow conical — The penumbra, or partial shadow 
— ^Eclipses of the sun not universal — Breadth of the lunar shadow 
on the earth — Primaries never eclipse each other — Duration of 
total eclipses — Solar and lunar ecliptic limits — Detail of several 
eclipses— Eclipse of 585 B. C— of 434 B. C— of 383 B. C— of 201 
B. C— Two mentioned by Dionysius — Chinese customs respecting 
eclipses— Eclipse of 1560— of May, 1706 — of April, 1715 — of June, 
1406 — Annular eclipse of 1836 — Number of eclipses in a year — 
Particular explanation of eclipses — How afiected by the position 
of the earth's axis^Use of eclipses in astronomy, geography, and 
chronology — Darkness at the crucifixion — Occupations. 

Of all the phenomena of the heavens, there are 
none that have more engaged the attention of man- 
kind than eclipses of the sun and moon; and to 
those unacquainted with astronomical principles, 
nothing appears more extraordinary than the 
accuracy with which they can be predicted. In 
the early ages, ere religion and science had en- 
lightened the world, appearances of this kind were 
generally regarded as alarming deviations from the 
established laws of nature, and but few, even among 
philosophers themselves, were able to account for 
them. At length, when men began to appl}'- them- 
selves to observations, and the celestial motions 
were better understood, these phenomena were 
found to depend upon a regular cause, and to admit 
of a natural and easy solution. 

To enter into a popular explanation of all parts 



of this doctrine would be impracticable. We shall 
therefore only attempt to give a general idea of the 
subject, and to show, without the embarrassment of 
calculations, the foundation upon which it depends. 
In the first place, all opaque or dark bodies, when 
they are exposed to the light of the sun, cast a 
shadow in the opposite direction ; and, as the earth 
is a body of this kind, whose shadow extends over a 
large space, and to a great distance, it is plain 
that if the moon in its orbit passes into this shadow 
it must be deprived of light, and suffer an eclipse. 

The plate represents, in the simplest and most 
intelligible manner, a total eclipse of the moon : 
the earth represented as stationary, with a conical 
shadow, whose base rests on the globe, and whose 
vertex is beyond the lunar orbit — the moon still 
remaining visible, though its light is dimmed. 
Nor is this last appearance merely pictorial, for 
there is generally some light discernible on the 
whole face of the moon, even during a total eclipse. 
Its surface is feebly illuminated with a reddish light 
resembling that of the clouds after sunset. This 
light proceeds from the solar rays refracted by the 
earth's atmosphere, and bent to such a degree as 
to pass into the shadow, those rays which are not 
sufficiently refracted to reach the surface of the 
earth, where they would be absorbed, continuing 
on their course. After they have traversed the 
atmosphere, they are bent behind the earth, and 



MW^WBKMi'.aW.WWMM.^^.giJHM-.-Wffi^iJCg Wg'aw'^.fc^vg 



WONDERS OF THE HEAVENS. 



225 




29 



UBBhirfrg^HBaaBW 



226 



WONDERS OF THE HEAVENS. 



tend, as it were, to the focus of a lens ; and some of 
them reach the moon, even when the earth is 
directly interposed between it and the sun so as to 
prevent its reception of any light independently of 
this inflection of rays. If the light thus tending to 
a point behind the earth were not in a great degree 
absorbed by the atmosphere, its effect would be 
very considerable ; for, if we consider one of the 
luminous points of the sun's disc, this point could 
only send directly a single ray to each point of 
space, but the effect of the earth's atmosphere is 
to cause a cone of luminous rays to fall behind the 
earth. The consequence is, that in most eclipses 




the obscured part of the moon is more or less 
faintly visible. The degree in which this takes 
place depends much on the general state of the 
earth's atmosphere at the time. The red rays, 
having the greatest momentum, are those which 
principally find their way to the moon. Thus, in 
the eclipse of September 2d, 1830, the moon 
appeared, at some places, of a deep blood-red color, 
even during the period of the greatest obscuration. 

A lunar eclipse being occasioned by the interpo- 
sition of the earth between the sun and moon, is an 
actual deprivation of light to the moon. It there- 
fore is for the time really dimmed, not merely in 
appearance to a spectator at some particular place, 
but absolutely and universally. We have no 
occasion, therefore, to refer to any particular point 
on the surface of the earth, or to embarrass our- 
selves with any considerations of difference between 
observations made at different places. We have 
only to ascertain when the light transmitted to the 
moon from the sun actually fails. 

The farther the earth is from the sun, the more 
slowly do the lines joining them, or the boundaries 
of the shadow, approach each other, and the larger, 
therefore, is the shadow at the moon's distance; 



and, besides this, the nearer the moon is to the 
earth, the larger, all other things continuing the 
same, is the part of the shadow through which it 
passes. On both accounts, the duration of an eclipse 
is greatest when the moon is at the least, and the 
sun at the greatest, distance from the earth. 

We have thus far spoken of the shadow as coni- 
cal ; and it is true that the portion of space in 
which the earth will entirely conceal the sun from 
the moon is so. But it is clear that there will be 
another portion in which part of the sun will be 
concealed, or there will be a partial shadow beyond 
the outline of the darker conical shadow. This 
partial shadow, called technically the penumbra, will 
be a portion of a cone. This appearance is repre- 
sented in the subjoined plate by the lighter shading 
on each side of the shadow proper. It exists both 
in the earth and the moon. In this plate, the earth 
is represented in three different points of its orbit. 
In the first, the moon is represented as advancing 
in her orbit after an eclipse of the sun. In the 
second, an eclipse of the sun is actually in progress ; 
and to that part of the earth where the dark conical 
shadow rests, the solar eclipse is total ; to that 
represented as covered by the fainter shadow, the 
eclipse is partial ; as respects the rest of the earth, 
there is no eclipse. In the third position of the 
earth, the moon is undergoing a total eclipse ; and it 
disappears or becomes dim to all those parts of the 
earth that are turned towards it. The reader is to 
bear in mind that both bodies move in their orbits 
from west to east, that is, as far as respects the 
plate, from left to right. 

We do not consider a lunar eclipse to take place 
when the moon is enveloped in this partial shadow 
merely, nor until some part of thai luminary is 
entirely darkened. The lunar ecliptic limits, 
therefore, are not affected by them. But it is of 
importance to observe that the penumbra does exist, 
and that in proportion as the moon is nearer the 
absolute shadow, the proportion of the sun obscured 
to her is increased. The penumbra, therefore, in- 
creases in depth, or the brilliancy of the moon dimin- 
ishes, as we approach the boundary of the dark part 
of the moon ; and this appearance may actually be 



228 



WONDERS OFTHE HEAVENS 



observed during a lunar eclipse, the brilliancy of the 
moon decreasing near the part that has disappeared. 

If the earth and sun were equally large, the 
earth's shadow would be infinitely extended, and 
all the way of the same size ; and the planet Mars, 
in either of its nodes and opposite to the sun, 
would be eclipsed in the earth's shadow. Were 
the earth larger than the sun, its shadow would 
increase in size the farther it extended, and would 
eclipse the planets Jupiter and Saturn, with all 
their moons, when they were opposite to the sun. 
But as Mars in opposition never falls into the 
earth's shadow, although it is not then above fifty- 
one millions of miles from the earth, it is plain that 
the earth is much less than the sun; for otherwise 
its shadow could not end in a point at so small a 
distance. If the sun and moon were equally large, 
the moon's shadow would reach the earth with ' an 
equal breadth, and cover a portion of the earth's 
surface more than two thousand miles broad, even 
if it fell directly against the earth's centre, as seen 
from the moon, and much more if it fell obliquely 
on the earth. But the moon's shadow is seldom one 
hundred and fifty miles broad at the earth, unless 
when it falls very obliquely on the earth, in total 
eclipses of the sun. In annular eclipses, the 
moon's real shadow ends in a point at some distance 
from the earth. The moon's small distance from 
the earth, and the shortness of its shadow, prove it 
to be less than the sun. And, as the earth's 
shadow would be large enough to cover the moon, 
even if the moon's diameter was three times as 
large as it is, it is plain that the earth is much 
larger than the moon. 

Though all opaque bodies on which the sun 
shines have their shadows, yet such is the bulk of 
the sun, and the distances of the planets, that the 
primary planets can never eclipse one another. A 
primary can eclipse only its secondary, or be 
eclipsed by it. 

For the sake of greater clearness, we have hith- 
erto spoken of the moon's orbit as if it were coin- 
cident with the plane of the ecliptic, in which the 
earth always moves, and the sun appears to move. 
In this case, the moon's shadow would fall upon 



the earth at every change, and eclipse the sun to 
some parts of the earth. In like manner, the moon 
would go through the middle of the earth's shadow, 
and be eclipsed, at every full ; but with this differ- 
ence, that the moon would be totally darkened for 
above an hour and a half, whereas the sun never 
was more than eight minutes totally eclipsed by 
the interposition of the moon. But one half of the 
moon's orbit is elevated five and one seventh degrees 
above the ecliptic, and the other half as much 
depressed below it ; consequently, the moon's orbit 
intersects the ecliptic in two opposite points, called 
the moon's nodes, as has been already noticed. 
When these points are in a right line with the 
centre of the sun at ncAV or full moon, the sun, 
moon, and earth are all in a right line; and if the 
moon be then new, its shadow falls upon the earth 
— if full, the earth's shadow falls upon the moon. 
When the sun and moon are more than seventeen 
degrees from either of the nodes at the time of con- 
junction, the moon is then generally too high or too 
low in its orbit to cast any part of its shadow on 
the earth ; and when the sun is more than twelve 
degrees from either of the nodes at the time of full 
moon, the moon is generally too high or too low in its 
orbit to go through any part of the earth's shadow; 
and in both these cases there will be no eclipse. 
But when the moon is less than seventeen degrees 
from either node at the time of conjunction, its 
shadow or penumbra falls more or less upon the 
earth as it is more or less within this limit; and 
when it is less than twelve degrees from either node 
at the time of opposition, it goes through a greater 
or less portion of the earth's shadow as it is more 
or less within this limit. Its orbit contains three 
hundred and sixty degrees, of which seventeen 
(the limit of solar eclipses on either side of the 
nodes) and twelve (the limit of lunar eclipses) are 
but small portions ; and as tlie sun commonly passes 
by the nodes but twice in a year, it is no wonder 
that we have so many new and full moons without 
eclipses. 

To illustrate this, let A B C D be the ecliptic, 
R S T U a circle lyiiig in the same plane with the 
ecliptic, and V W X Y the moon's orbit, all thrown 



WONDERS OF THE HEAVENS. 



229 



into an oblique view, which gives them an elliptical 
shape to the eye. One half of the moon's orbit, at 
V W X, is always below the ecliptic, and the other 
half X Y V above it. The points V and X, where 
the moon's orbit intersects the circle R, S T U, which 
lies even with the ecliptic, are the moon's nodes; 
and a right line, as X E V, drawn from one to the 
other through the earth's centre, is the line of the 
nodes, which is carried almost parallel to itself round 
the sun in a year. 

If the moon moved round the earth in the orbit 



E, S T U, which is coincident with the plane of the 
ecliptic, its shadow would fall upon the earth every 
time it is in conjunction with the sun, and at every 
opposition it would go through the earth's shadow. 
Were this the case, the sun would be eclipsed at 
every change, and the moon at every full, as 
already mentioned. 

But although the moon's shadow N must fall 
upon the earth at a when the earth is at E and 
the moon in conjunction with the sun at i, because 
it is then very near one of the nodes, and at oppo- 




sition n must go through the earth's shadow I, 
because it is then near the other node, yet, in the 
time that it goes round the earth to the next change 
according to the order of the letters X Y V W, the 
earth advances from E to e according to the order 
of the letters E F G H, and the line of the nodes 
VEX, being carried nearly parallel to itself, brings 
the point / of the moon's orbit in conjunction with 
the sun at that next change, and then the moon. 



being at/, is too high above the ecliptic to cast a 
shadow on the earth; and as the earth is still 
moving forward, the moon at the next opposition 
will be at g, too far below the ecliptic to go through 
any part of the earth's shadow, for by that time 
the point g will be at a considerable distance from 
the earth as seen from the sun. 

When the earth comes to F, the moon in con- 
junction with the sun Z is not at k, in a plane 



230 



WONDERS OF THE HEAVENS 



coincident with the ecliptic, but above it at Y in 
the highest part of the orbit, and then the point b 
of the shadow goes far above the earth. The 
moon at the next opposition is not at o but at W, 
where the earth's shadow goes far above her. In 
both these cases the line of the nodes V F X is 
about ninety degrees from the sun, and both lumi- 
naries are as far as possible from the limits of 
eclipses. 

When the earth has gone half round the ecliptic 
from E to G, the line of the nodes V G X is nearly, 
if not exactly, directed towards the sun at Z ; and 



then the new moon I casts its shadow P on the 
earth G, and the full moon p goes through the 
earth's shadow L, which brings on an eclipse 
again, as when the earth was at E. 

When the earth comes to H, the new moon does 
not happen at m in a plane coincident with the 
ecliptic C D, but at W below it, and then the 
shadow Q, goes far below the earth. At the next 
full, the moon is not at q but at Y, five and one 
seventh degrees above q, and at its greatest height 
above the ecliptic C D, being then as far as possi- 
ble, at any opposition, from the earth's shadow M.* 




If the line of the nodes, like the earth's axis, was 
carried parallel to itself round the sun, there would 
be just half a year between the conjunctions of the 
sun and nodes. But the nodes shift backward, or 
contrary to the earth's annual motion, nineteen and 
one third degrees every year, and, therefore, the 
same node comes round to the sun nineteen days 
sooner every year than on the year before. Con- 
sequently, from the time that the ascending node 
passes by the sun as seen from the earth, it is only 
one hundred and seventy-three days (not half a 
year) till the descending node passes by him. 
Therefore, in whatever time of the year we have 
eclipses of the luminaries about either node, we 
may be sure that in one hundred and seventy- 
three days afterward we shall have eclipses about 
the other node. 

It is particularly to be noted that eclipses which 
have happened many centuries ago, will not be 
found by our present tables to agree exactly with 
ancient observations, by reason of the great anoma- 
lies in the lunar motions. 

We are credibly informed, from the testimony of 
the ancients, that there was a total eclipse of the 
sun predicted by Thales to happen, in the fourth 



year of the 48th Olympiad, either at Sardis or 
Miletus, in Asia, where Thales then resided. 
That year corresponds to the 585th year before 
Christ; when, accordingly, there happened a very 
signal eclipse of the sun, on the 28th of May, 
answering to the present 10th of that month, 
central through North America, the south parts of 
France, Italy, &c., as far as Athens, or the isles in 
the iEgean sea, which is the farthest that even 
the Caroline Tables carry it, and consequently 
make it invisible to any part of Asia in the total 
character, though we have good reason to believe 
that it extended to Babylon, and went down central 
over that city. We are not, however, to imagine 
that it was set before it past Sardis and the Asiatic 
towns, where the predictor lived, because an invis- 
ible eclipse could have been of no service to 
demonstrate his ability in astronomical sciences to 
his countrymen, as it could give no proof of its 
reality. 

Thucydides relates that a solar eclipse happened 
on a summer's day, in the afternoon, in the first 
year of the Peloponnesian war, so great that the 

* In some parts of the explanatioa the two preceding plates are 
referred to in connection, the latter being an edge view of the former. 



WONDERS OF THE HEAVENS. 



231 



1 



stars appeared. Rhodius was victor in the Olympic 
games the fourth year of the said war, being also 
the fourth of the 87th Olympiad ; so that the 
eclipse must have happened in the 431st year before 
Christ. And by computation it appears that on 
the 3d of August there was a signal eclipse which 
would have past over Athens, central about six in 
the evening, but which our present tables bring no 
farther than the ancient Syrtes, on the African coast, 
above four hundred miles from Athens, which, 
suffering in that case but nine digits, could by no 
means exhibit the remarkable darkness recited by 
this historian. The centre, therefore, seems to have 
past Athens about six in the evening, and probably 
might go down about Jerusalem, or near it, con- 
trary to the construction of the present tables. 

There are two ancient eclipses of the moon 
recorded by Ptolemy from Hipparchus. The first 
of these was observed at Babylon, December 22d, 
in the year before Christ 383, when the moon 
began to be eclipsed about half an hour before the 
sun rose, and the eclipse was not over before the 
moon set ; but by most of our astronomical tables 
the moon was set at Babylon half an hour before the 
eclipse began, in which case there could have 
been no possibility of observing it. The second 
eclipse was observed at Alexandria, September 
22d, the year before Christ 201, where the moon 
rose so much eclipsed that the eclipse must have 
begun about half an hour before she rose; whereas, 
by most of our tables, the beginning of this eclipse 
was not till about ten minutes after the moon rose 
at Alexandria. Had these eclipses begun and 
ended while the sun was below the horizon, we 
might have imagined, that, as the ancients had no 
certain way of measuring time, they might have 
been so far mistaken in the hours that we could 
not have laid any stress on the accounts given by 
them. But as in the first eclipse the moon was 
set, and consequently the sun risen, before it was 
over — and in the second eclipse the sun was set, 
and the moon not risen, till some time after it 
began, — these are such circumstances as the 
observers could not possibly be mistaken in. 
Many other remarkable eclipses are spoken of 



by the ancients, and if their relations could be de- 
pended on they would be of great use in chronology. 
Dionysius, of Halicarnassus, mentions two total 
eclipses of the sun, that happened, one at the birth 
of Romulus, and the other at his death; in each of 
which the obscurity was as great as in the darkest 
night. But this account, like that of the prodigies 
which were seen at the time of Caesar's death, 
deserves very little credit. In ancient times, every 
great event was said to have been accompanied by 
comets or other portentous appearances; and 
eclipses of the sun, in particular, were always re- 
garded as calamitous omens, presaging the death 
of kings or some illustrious character. This super- 
stition is frequently alluded to by the poets. Milton 
says that the sun 

" From behind the moon^ 
la dim eclipse, disastrous twilight sheds 
On half the nations, and with fear of change 
Perplexes monarchs." 

In China, where astronomy is made subservient 
to the interest of the state, they have particular 
ceremonies appropriated to those days on which 
eclipses are to take place, and both the prince and 
the people are scrupulously exact in their ob- 
servance. The chief of the "tribunal of mathe- 
matics" is there a grand but a dangerous appoint- 
ment, for under the reign of one of their monarchs 
the two principal astronomers were condemned to 
death on account of their negligence in omitting 
to announce the precise time of an eclipse. 

A total eclipse of the sun is an extraordinary 
spectacle. Clavius, who observed that which 
happened at Coimbra, in Portugal, on the 21st of 
August, 1560, informs us that the obscurity was 
greater, or at least more striking and sensible, 
than that of the night. "It was so dark, for a short 
time, that he could scarcely see his hand," some of 
the stars made their appearance for two or three 
minutes, and the birds were so terrified that they 
fell to the ground. On May 12th, 1706, a total 
eclipse of the sun was observed at Geneva. Though 
the sky was somewhat overcast, the heat of the sun 
was already felt when the eclipse began. But 



232 



WONDERS OF THE HEAVENS 



quite a sensible coldness took place, and the light 
evidently decreased as the moon gradually covered 
a greater and greater part of the sun. When that 
body was nearly covered, the bright crescent was 
visible until it became very narrow, when it disap- 
peared instantaneously, and, in a twinkling, the 
eclipse was total. The darkness, which was already 
considerable, became much greater. The clouds 
suddenly changed color, first becoming red and 
then a pale violet. During the whole time of the 
total immersion, a whiteness was seen, which seemed 
to break out from behind the moon, and to encom- 
pass it equally on all sides, in breadth less than a 
twelfth part of the moon's diameter. This secondary 
appeared very black, and its disc very well defined 
within the whiteness. Venus was visible in a north- 
easterly direction from the sun. Saturn and Mer- 
cury were also seen, by many persons, eastward of 
the sun. If the sky had been clear, Jupiter and 
Mars, and many more of the heavenly bodies, would 
have been visible. And, indeed, some one in the 
country counted more than sixteen stars. To those 
who were on high land, the sky, where it was not 
overcast, seemed in all respects like the nocturnal 
sphere during full moon. The total immersion 
began about three quarters after nine. The dura- 
tion of total darkness was three minutes, when the 
first ray shot forth with much splendor. A little 
after the sun began to appear, the whiteness 
mentioned above entirely vanished. Just before 
the total obscuration, the country to the west of the 
observer already appeared overcast with darkness ; 
and, after the total obscuration was past, he per- 
ceived, the country to the east in like manner 
darkened. An observer of the same eclipse at 
Berne, stated that the sun was totally darkened 
for four and a half minutes, and that its immersion 
was preceded by a blood-red streak of light from 
its left limb, which continued about seven seconds, 
and then, all of a sudden, a part of the sun's disc 
appeared brighter than Venus was ever seen in the 
night, and in that very instant gave a light and a 
shadow to objects as strong as ever moonlight 
does. 

In 1715, April 22d, Halley, having found, by 



comparing what had been before observed of solar 
eclipses, that the whole shadow would fall upon 
England, thought it a good opportunity to have 
the dimensions of the shadow ascertained from 
observation. He therefore caused maps containing 
the calculated limits of the eclipse to be distributed 
in the different towns, with a request that the phe- 
nomena attending it might be observed. 

His own observations were made at London. 
The eclipse there began at six minutes after eight. 
From that moment, the eclipse advancing was about 
ten digits at nine o'clock, when the face and color 
of the sky gradually changed from a perfectly 
serene azure to a dusky livid color, with a slight 
tinge of purple intermixed, and grew darker and 
darker till the total immersion, which happened at 
nine minutes after nine o'clock. It was universally 
observed that when the last part of the sun (the 
east side) remained alone visible, it grew very dim, 
and was easily supportable by the unshaded eye, 
even through the telescope, for more than a minute 
preceding the total darkness. But the eye could 
not endure the splendor of the emerging beams from 
the first moment in the telescope. To this, perhaps, 
two causes concurred. One, that the pupil of the 
eye had dilated during the darkness ; the other, that 
the eastern part of the moon, having been heated by 
the long-continued action of the sun, would have an 
atmosphere replete with vapors, while the western 
limb had endured as long a night, during which all 
the vapors would have fallen in dews, and its atmo- 
sphere would be pure and transparent. A few 
seconds after the sun was totally covered, there 
was visible round the moon a luminous ring, in 
breadth about a tenth part of the moon's diameter. 
It was of a pale white or rather pearl color, seeming 
a little tinged with the colors of the iris, and con- 
centric with the moon. Whatever was its cause, 
this ring appeared much brighter and whiter near 
the body of the moon than at a distance from it, 
and its external circumference, which was ill defined, 
seemed terminated only by the extreme rarity of the 
matter of which it was composed, and in all respects 
resembled in appearance an enlightened atmo- 
sphere viewed from a distance. About two or three 



WONDERS OF THE HEAVENS. 



233 



seconds before the emersion, on the western side of 
the moon, where the sun was about to appear, 
Halley observed a long and very narrow streak of 
a dusky, but strong red light, seeming to color the 
dark edge of the moon. But this instantly vanished, 
as well as the white ring, on the first appearance of 
the sun. 

The degree of darkness was not very great. It 
was such, however, that Venus, Jupiter, and Mer- 
cury became visible, and, among the fixed stars, 
Aldebaran and Capella. The darkness was more 
perfect in those places that were near the centre 
of the shadow, in some of which more than twenty 
stars became visible. At London, the lower parts 
of the hemisphere, particularly in the southeast, 
under the sun, had a crepuscular brightness, and all 
around so much of the atmosphere as was above 
the horizon and without the cone of the moon's 
shadow was more or less enlightened by the sun's 
beams, and its reflection gave a diffused light, which 
made the air seem hazy, and prevented the appear- 
ance of the stars. 

Total eclipses, however, happen but seldom at 
any particular place, and annular eclipses are 
equally uncommon. There was a remarkable annu- 
lar eclipse visible in Europe, in April, 1764. Total 
eclipses are so rare, that Halley, in his account 
of the above eclipse, observes " that although 
twenty-eight eclipses of the sun happen in eighteen 
years, and of these eight pass over the parallel 
of London, yet from 1140 to 1715 no total eclipse 
of the sun had been seen in that metropolis." It 
may be added that in annular eclipses, as well as 
in all those that are not total, the degree of dark- 
ness that takes place is not so considerable as per- 
sons are apt to imagine. Maclaurin, in his account 
of the annular eclipse which happened at Edinburg 
in 1737, states that during the appearance of the 
ring daylight was not greatly obscured, appearing 
only as much dimmer than usual as it does during 
a gentle mist in an April morning. And Le 
Monnier, who went from France to England on 
purpose to observe the annular eclipse which 
happened in 1748, says, that, during the middle of 

the eclipse, he could perceive nothing on the sun, 
30 



when he looked at it with his naked eyes, but saw 
it full, though faint in its light. 

June 16th 1806, a total eclipse of the sun was 
observed in various parts of this country. The 
following is by an observer stationed at Kinder- 
hook, state of New York. First interior contact, or 
total obscurity, took place at ten hours fifty- 
five minutes and fifty-eight seconds, at the distance 
of fifty degrees from the right superior vertex. 
Four or five seconds before the total obscurity, 
the remainder of the sun's disc was reduced to a 
very short line, interrupted in many places. The 
darkened glass with which this phenomenon was 
observed, was sufficiently clear to distinguish terres- 
trial objects. After this observation, the colored 
glass was laid aside in order to observe the end of 
total darkness. The moon was closely observed 
during two minutes without the appearance of a 
single luminous point in its disc. But the disc had 
round it a ring or illuminated atmosphere, which 
was of a pearl color, and projected six minutes from 
the limb. The diameter of this ring was estimated 
at forty-five minutes. The darkness was not so 
great as had been expected, the light being proba- 
bly greater than that of the full moon. From the 
extremity of the ring, many luminous rays were 
projected to more than three degrees' distance. 
The lunar disc was ill-defined, and very dark, 
forming a contrast with the luminous ring. With a 
telescope, some appearances like very slender 
columns of smoke were distinguished issuing from 
the western part of the moon. During the whole 
eclipse the sky was very clear, not a single cloud 
being visible, and there was scarcely any wind. 
The sun was without a spot. A little dew fell 
during the darkness. Five or six principal stars 
and planets were visible. The plate accompanying 
represents the total eclipse. The luminous ring 
round the moon is exactly as it appeared in the 
middle of the eclipse. The illumination which is 
seen in the lunar disc preceded the appearance of 
the first rays of the sun by about seven seconds. 
Two minutes before the emersion the observer fixed 
his eye on the point whence it was to proceed, and, 
as the field of his telescope did not embrace more 



li^AiKfUEtaSBB! 



234 



WONDERS OF THE HEAVENS 



than a third part of the disc, he could not observe 
whether the circumference of the ring was diminish- 
ed on the opposite side. In the part where the 
emersion took place, the ring Avas illuminated by 
degrees, and the atmosphere was more dense and 
brilliant near the edge of the moon. A little before 
the illumination of the lunar disc, a zone was 
observed to issue, concentric with the sun, and 



similar in appearance to a cloud illuminated by the 
sun's rays. It is represented in the plate. But in 
order to have a proper conception of what is intended 
to be represented, we must transfer our ideas to the 
heavens, and imagine, at the departure of the last 
ray of the sun in its retreat behind the moon, an 
awful gloom immediately diffused over the face of 
nature, and round a dark circle near the zenith 




an immense radiated glcrry, like a new creation, in 
a moment bursting on the sight, and for several 
minutes fixing the gaze of man in silent amaze- 
ment. 

An English paper gives the following description 
of the appearance of the sun and moon during the 
annular eclipse of those luminaries, on May 15, 
1836 :— 



A singularly beautiful appearance was exhibited 
by the telescopes at the instant of the completion 
of the ring. The two horns or points of the une- 
clipsed part of the sun had been gradually approach- 
ing each other till their distance had become small. 
Instead, however, of continuing to make this gradual 
approach, there seemed to issue from each great 
numbers of beads of light, resembling drops of quick- 



WONDERS OF THE HEAVENS 



235 



silver, or a line of electric sparks, and in an instant 
the ring was completed. This seems obviously to 
establish, what appears on other considerations to 
be very likely, that the limbs of the sun and moon 
are not the fine and perfectly regular curves that 
they appear to be, but that they are full of numerous 
minute inequalities. The appearance of the ring 
was peculiarly striking and beautiful. The sun's 
whole central parts were blotted out, and all that 
remained of his magnificent orb was a small but 
brilliant rim of light. 

Murray, a well-known scientific lecturer, furnishes 
some further interesting particulars connected with 
this phenomenon : — 

During the period of the eclipse, insect life was 
still and motionless. The birds of the air flew near 
the ground, and there was a peculiar solemnity in 
the silence that reigned around, unbroken save 
by the song of the lark which rose at intervals. 
Even the "attic warbler," was still, however, dur- 
ing the greatest obscuration. At the close of the 
eclipse, numerous insects appeared, and the lark 
soared higher Avith its welcome note. The atmo- 
sphere had been almost free from clouds ; but float- 
ing cumuli collected and condensed, and toward the 
close of the eclipse had rallied, as if in sympathy, 
round the standard of the sun. The diminution of 
light was by no means so great as many had 
expected. No stars were visible. Venus, perhaps, 
might have been seen, save that clouds intercepted 
her path. The light during the greatest obscura- 
tion of the sun was quite peculiar. Nature assumed 
a lurid aspect, and the sea, too, had a livery different 
from its usual tone of color. It was not a twilight 
hue: it was " itself alone" — such as I have seen in 
looking through a Claude-Lorraine glass. The 
prophet's language describes it: "The light was 
neither clear nor dark." "It was not day nor night." 
During the solar eclipse of 1820, I was among 
the serpentine rocks near Portsoy, Scotland ; and 
the diminution of light on that occasion seemed 
greater than in the present instance. 

In any year, the number of eclipses of both 
luminaries cannot be less than two, nor more than 
seven. The most usual number is four, and it is very 



rare to have more than six. For the sun passes by 
both the nodes but once a year, unless he passes 
by one of them in the beginning of the year ; and if 
he does, he will pass by the same node again a little 
before the year be finished ; because, as these points 
move nineteen and one third degrees backward 
every year, the sun will come to either of them one 
hundred and seventy days after the other; and 
when either node is within seventeen degrees of 
the sun at the time of new moon, the sun will be 
eclipsed. At the subsequent opposition, the moon 
will be eclipsed in the other node, and come round 
to the next conjunction again ere the former node 
be seventeen degrees past the sun, and will there- 
fore eclipse him again. When three eclipses fall 
about either node, the like number generally fall 
about the opposite, as the sun comes to it in one 
hundred and seventy-three days afterward ; and six 
lunations contain but four days more. Thus there 
may be two eclipses of the sun, and one of the moon, 
about each of her nodes. But when the moon 
changes in either of the nodes, she cannot be near 
enough to the other node at the next full to be eclips- 
ed; and in six lunar months afterward she will 
change near the other node. In these cases there 
can be but two eclipses in a year, and they are 
both of the sun. 

A longer period for comparing and examining 
eclipses which happen at intervals of time, is five 
hundred and fifty-seven years twenty-one days 
eighteen hours thirty minutes eleven seconds, in 
which time there are six thousand eight hundred 
and ninety mean lunations, and the sun and node 
meet again so nearly as to be but eleven seconds 
distant; but then it is not the same eclipse that 
returns, as in the shorter period above mentioned. 

Before the cause of eclipses was explained to the 
world at large, and shown to be a natural and 
necessary phenomenon, astrologers and crafty men 
took advantage of the terror they inspired to keep 
the multitude in slavish subjection to their will. 
Treatises were written to show against what 
regions the malevolent effects of any particular 
eclipse was aimed; and the writers aflfirmed that 
the effects of an eclipse of the sun continued as 



236 



WONDERS OF THE HEAVENS 



many years as the eclipse lasted hours, and that 
of the moon as many months. 

Such idle notions were once of no small advantage 
to Christopher Columbus, who, in the year 1493, 
was driven on the Island of Jamaica, where he was 
in the greatest distress for want of provisions, and 
was moreover refused any assistance from the in- 
habitants; on which he threatened them with a 
plague, and told them, that, in token of it, there 
should be an eclipse, which accordingly happened 
on the day he had foretold, and so terrified the 
barbarians that they strove who should be first in 
bringing him all sorts of provisions, throwing them 
at his feet, and imploring his forgiveness. 

Eclipses of the sun are more frequent than those of 
the moon, because the sun's ecliptic limits are greater 
than the moon's ; yet we have more visible eclipses 
of the moon than of the sun, because eclipses of the 
moon are seen from all parts of that hemisphere of 
the earth which is next her, and are equally great 
to each of those parts ; but the sun's eclipses are 
visible only to that small portion of the hemisphere 
next him whereon the moon's shadow falls. 

The moon's orbit being elliptical, and the earth 
in one of its foci, it is once at its least distance from 
the earth, and once at its greatest, in every luna- 
tion. When the moon changes at its least distance 
from the earth, and so near the node that its dark 
shadow falls upon the earth, it appears large enough 
to cover the whole disc of the sun from that part on 
which her shadow falls, and the sun appears totally 
eclipsed there for some minutes. But when the moon 
changes at its greatest distance from the earth, and 
so near the node that the dark shadow is directed 
towards the earth, its diameter subtends a less angle 
than the sun's, and therefore it cannot hide the 
whole disc from any part of the earth, nor does the 
shadow reach it at that time ; and to the place over 
which the point of the shadow hangs the eclipse is 
annular, the sun's edge appearing like a luminous 
ring all around the body of the moon. When the 
change happens within seventeen degrees of the 
node, and the moon at her mean distance from the 
earth, the point of the shadow just touches the 
earth, and eclipses the sun totally to that small 



spot whereon the shadow falls ; but the darkness is 
not of a moment's continuance. 

The moon's apparent diameter when largest 
exceeds the sun's when least only one minute and 
thirty-eight seconds of a degree ; and in the greatest 
eclipse of the sun that can happen at any time and 
place, the total darkness continues no longer than 
whilst the moon is going one minute and thirty-eight 
seconds from the sun in her orbit, which is about 
three minutes and thirteen seconds. 

The moon's dark shadow covers only a spot on 
the earth's surface about one hundred and eighty 
miles broad when the moon's diameter appears 
largest and the sun's least, and the total darkness 
can extend no farther than the dark shadow covers. 
Yet the moon's partial shadow or penumbra may 
then cover a circular space four thousand and nine 
hundred miles in diameter, within all which the sun 
is more or less eclipsed as the places are less or 
more distant from the centre of the penumbra. 
When the moon changes exactly in the node, the 
penumbra is circular on the earth at the middle of 
the general eclipse, because at that time it falls 
perpendicularly on the earth's surface ; but at every 
other moment it falls obliquely, and will therefore 
be elliptical, and the more so as the time is longer 
before or after the middle of the general eclipse, 
and then much greater portions of the earth's 
surface are involved in the penumbra. 

When the penumbra first touches the earth, the 
general eclipse begins: when it leaves the earth, 
the general eclipse ends: from the beginning to 
the end the sun appears eclipsed to some portion 
of the earth. When the penumbra touches any 
place, the eclipse begins at that place, and ends 
when the penumbra leaves it. When the moon 
changes in the node, the penumbra goes over 
the centre of the earth's disc, as seen from the 
moon, and consequently, by describing the longest 
line possible on the earth, continues the longest 
upon it, namely, (at a mean rate,) five hours and 
fifty minutes — more, if the moon be at her greatest 
distance from the earth, because she then moves 
slowest ; less, if she be at her least distance, because 
of her quicker motion. 



J 



WONDERS OF THE HEAVENS 



237 



To make these and several other phenom- | moon, and AMP the moon's orbit. Draw the 
ena plainer, let S be the sun, E the earth, M the | right line W c 12 from the western side of the sun 




at W, touching the western side of the moon at c, 
and the earth at 12. Draw also the right line V c? 12 
from the eastern side of the sun at V, touching the 
eastern side of the moon at d, and the earth at 12. 
The dark space cel2d included between those lines 
is the moon's shadow ending in a point at 12, 
where it touches the earth, because in this case the 
moon is supposed to change at M, in the middle 
between A the apogee, or farthest point of her orbit 
from the earth, and P the perigee, or nearest point 
to it. For had the point P been at M, the moon 
had been nearer the earth, and her dark shadow at 
e would have covered a space upon it about one 
hundred and eighty miles broad, and the sun would 
have been totally darkened for some time; but had 
the point A been at M, the moon would have been 
farther from the earth, and her shadow would have 
ended in a point about e, and, therefore, the sun 
would have appeared like a luminous ring all 
around the moon. Draw the right lines W Xdb 
and V X c g, touching the contrary sides of the sun 
and moon, and ending on the earth at a and b; 
draw also the right line S X M 12 from the centre 
of the sun's disc, through the moon's centre, to the 
earth at 12; and suppose the two former lines 
WXdbdLudYXcg to revolve on the line SXM12 
as an axis, and their points a and b will describe 
the limits of the penumbra T T on the earth's 
surface, including the large space a ob 12 a, within 



which the sun appears more or less eclipsed as the 
places are more or less distant from the verge of 
the penumbra a ob. 

Draw the right line ?/ 12 across the sun's disc 
perpendicular to S X M, the axis of the penumbra ; 
then divide the line y 12 into twelve equal parts, 
as in the figure, for the twelve digits * of the sun's 
diameter, and, at equal distances from the centre 
of the penumbra at 12 (on the earth's surface Y Y) 
to its edge a ob, draw twelve concentric circles, as 
marked with the numeral figures 12 3 4, &c., and 
remember that the moon's motion in her orbit 
A M P is from west to east, as from s to t. Then, 
to an observer on the earth at b, the eastern 
limb of the moon at d seems to touch the western 
limb of the sun at W when the moon is at M, and 
the sun's eclipse begins at b, appearing as at A, 
(next figure ;) but, at the same moment of absolute 
time to an observer at a, in the previous figure, 
the western edge of the moon at c leaves the eastern 
edge of the sun at V, and the eclipse ends, as at 
the right hand G of the next figure. At the very same 
instant, to all those who live on the circle marked 1 
on the earth E in the last figure, the moon M cuts 
off" or darkens a twelfth part of the sun S, and 
eclipses him one digit, as at 1 in the next figure; to 
those who live on the circle marked 2 in the last 
figure, the moon cuts off two twelfth parts of the 

* A digit is a twelfth part of the diameter of the sun or moon. 



238 



WONDERS OF THE HEAVENS 



sun, as at 2 in the next figure ; to those on the cir- 
cle 3, three parts; and so on to the centre at 12, 



where the sun is centrally eclipsed, as at B in the 
middle of the next figure, under which there is a 




scale of hours and minutes to show, at a mean 
state, how long it is from the beginning to the end of 
a central eclipse of the sun, and how many digits 
are eclipsed at any particular time from the be- 
ginning at A to the middle at B, or the end at C. 
Thus, in sixteen minutes from the beginning, the 
sun is two digits eclipsed; in an hour and five 
minutes, eight digits; and in an hour and thirty- 
seven minutes, twelve digits. 

By the last figure but one, it is plain that the 
sun is totally or centrally eclipsed but to a small 
part of the earth at any time, because the dark 
conical shadow e of the moon M falls but on a small 
part of the earth, and that the partial eclipse is 
confined at that time to the space included by the 
circle a o 6, of which only one half can be projected 
in the figure, the other half being supposed to be 
hid by the convexity of the earth E; and, likewise, 
that no part of the sun is eclipsed to the large 
space Y Y of the earth, because the moon is not 
between the sun and any of that part of the earth, 
and therefore to all that part the eclipse is invisible. 
The earth turns eastward on its axis, as from g to h, 
which is the same way that the moon's shadow 
moves ; but the moon's motion is much swifter in 
her orbit from s to t, and, therefore, although 
eclipses of the sun are of longer duration on account 
of the earth's motion on its axis than they would be 
if that motion ceased, yet, in four minutes of time 
at most the moon's swifter motion carries her dark 
shadow quite over any place that its centre touches 
at the time of greatest obscuration. The motion 
of the shadow on the earth's disc is equal to the 
moon's motion from the sun, which is about thirty 



and a half minutes of a degree every hour, at a mean 
rate ; but so much of the moon's orbit is equal to 
thirty and a half degrees of a great circle on the 
earth, and therefore the moon's shadow goes thirty 
and a half degrees, or eighteen hundred and thirty 
geographical miles, on the earth in an hour, or 
thirty and a half miles in a minute, which is nearly 
four times as swift as the motion of a cannon-ball. 

As seen from the sun or moon, the earth's axis 
appears differently inclined every day of the year, 
on account of keeping its parallelism throughout its 
annual course. Let E, D, 0, N (next figure) be 
the earth at the two equinoxes and the two sol- 
stices, N S its axis, N the north pole, S the south 
pole, M Q the equator, T the tropic of cancer, 
t the tropic of Capricorn, and ABC the circumfer- 
ence of the earth's enlightened disc as seen from 
the sun or new moon at these times. The earth's 
axis has the position N E S at the vernal equinox, 
lying towards the right hand, as seen from the sun 
or new moon, its poles N and S being then in the 
circumference of the disc, and the equator and all 
its parallels seem to be straight lines, because their 
planes pass through the eye of an observer looking 
down on the earth from the sun or moon directly 
over E, where the ecliptic F G intersects the equa- 
tor M. At the summer solstice, the earth's axis 
has the position N D S, and that part of the ecliptic 
F G, in which the moon is then new, touches the 
tropic of cancer T at D. The north pole N, at that 
time inclining twenty-three and a half degrees to- 
wards the sun, falls so many degrees within the 
earth's enlightened disc, because the sun is then 
vertical to D twenty-three and a half degrees north 



WONDERS OF THE HEAVENS. 



239 



of the equator JE Q; and the equator and all its 
parallels seem elliptic curves bending downward, or 
towards the south pole, as seen from the sun, which 
pole, together with twenty-three and a half degrees 
all around it is behind the disc in the dark hemis- 
phere of the earth. At the autumnal equinox, the 
earth's axis has the position N S, lying to the left 
hand, as seen from the sun or new moon, which are 
then vertical to 0, where the ecliptic cuts the equa- 
tor, ^E Q. Both poles now lie in the circumference 
of the disc, the north pole just going to disappear 
behind it, and the south pole just entering into it, 
and the equator and all its parallels seem to be 
straight lines, because their planes pass through 



the observer's eye, as seen from the sun, and very 
nearly so as seen from the moon. At the winter 
solstice, the earth's axis has the position N N S, 
when its south pole S, inclining twenty-three and a 
half degrees toward the sun, falls twenty-three and 
a half degrees within the enlightened disc, as seen 
from the sun or new moon, which are then vertical 
to the tropic of Capricorn t twenty-three and a half 
degrees south of the equator JE Q, and the equator 
and all its parallels seem elliptic curves bending 
upward, the north pole being as far behind the disc 
in the dark hemisphere, as the south pole has 
advanced into the light. The nearer any time of 
the year is to the equinoxes or solstices, the more 




does it partake of the phenomena relating to them. 
Thus it appears that from the vernal equinox to 
the autumnal, the north pole is enlightened, and the 
equator and all its parallels appear elliptical, as 
seen from the sun, more or less curved as the time 
is nearer to or farther from the summer solstice, 
and bending downwards or tow^ards the South pole. 
The reverse of this happens from the autumnal 
equinox to the vernal. A little consideration will 
be sufficient to convince the reader that the earth's 
axis inclines towards the sun at the summer solstice, 
from the sun at the winter solstice, and sidewise 
to the sun at the equinoxes — towards the right 
hand, as seen from the sun, at the vernal equinox, 
and towards the left hand at the autumnal. From 
the winter to the summer solstice,. the earth's axis 
inclines more or less to the right hand, as seen from 



the sun, and the contrary from the summer to the 
winter solstice. 

The different positions of the earth's axis, as 
seen from the sun at different times of the year, 
affect solar eclipses greatly with regard to particular 
places — so far that they would make central eclipses 
which fall at one time of the year invisible if they 
fell at another, even though the moon should 
always change in the nodes, and at the same hour 
of the day, of which various affections we shall 
only give examples for the times of the equinoxes 
and solstices. 

In the above figure let F G be part of the ecliptic, 
and I K, i k, i k, i k, parts of the moon's orbit, (all 
seen edgewise, and therefore projected into right 
lines;) let the intersections N, 0, D, E be one 
and the same node at the above times, when the 



240 



WONDERS OF THE HEAVENS 



earth has the above-mentioned different positions ; 
and let the spaces included by the circles, P, p, p, p, 
be the penumbra at these times, as its centre is 
passing over the centre of the earth's disc. At the 
winter solstice, v^^hen the earth's axis has the posi- 
tion N N S, the centre of the penumbra P touches 
the tropic of Capricorn Hn N at the middle of the 
general eclipse; but no part of the penumbra 
touches the tropic of cancer T. At the summer 
solstice, when the earth's axis has the position 
N D S, (iD k being then part of the moon's orbit, 
whose node is at D,) the penumbra p has its centre 
at D, on the tropic of cancer T, at the middle of the 
general eclipse, and then no part of it touches the 
tropic of Capricorn t. At the autumnal equinox, 
the earth's axis has the position N S, {iO k being 
then part of the moon's orbit,) and the penumbra 
equally includes parts of both tropics T and t at the 
middle of the general eclipse. At the vernal equinox 
it does the same, because the earth's axis has the 
position N E S. But, in the former of these two last 
cases, the penumbra enters the earth at A, north of 
the tropic of cancer T, and leaves it at m, south of 
the tropic of Capricorn t, having gone over the 
earth obliquely southward, as its centre described 
the line A m; whereas, in the latter case, the 
penumbra touches the earth at n, south of the 
equator M Q,, and, describing the line nHq, (similar 
to the former line A w in open space,) goes 
obliquely northward over the earth, and leaves it 
at q, north of the equator. 

In all these circumstances, the moon has been 
supposed to change at noon in her descending node. 
Had she changed in her ascending node, the phe- 
nomena would have been as various the contrary 
way, with respect to the penumbra's going north- 
ward or southward over the earth. But because 
the moon changes at all hours, as often in one 
node as in the other, and at all distances from them 
both at different times, the variety of the phases of 
eclipses are almost innumerable, even at the same 
places. We must consider, also, how variously 
the same places are situated on the enlightened 
disc of the earth, with respect to the penumbra's 
motion, at the different hours when eclipses happen. 



When the moon changes seventeen degrees 
short of her descending node, the penumbra P 18 
just touches the northern part of the earth's disc, 
near the north pole N, and, as seen from that 
place, the moon appears to touch the sun, but hides 
no part of him from sight. Had the change been 
as far short of the ascending node, the penumbra 
would have touched the southern part of the disc 
near the south pole S. When the moon changes 
twelve degrees short of the descending node, more 
than a third part of the penumbra P 12 falls on the 
northern parts of the earth at the middle of the 
general eclipse. Had she changed as far past the 
same node, as much of the other side of the penum- 
bra about P would have fallen on the southern part 
of the earth, and all the rest in open space. When 
the moon changes six degrees from the node, 
almost the whole penumbra P 6 falls on the earth 
at the middle of the general eclipse. And, lastly, 
when the moon changes in the node at N, the 
penumbra P N takes the longest course possible on 
the earth's disc, its centre falling on the middle 
thereof at the middle of the general eclipse. The 
farther the moon changes from either node, (within 
seventeen degrees of it,) the shorter is the penum- 
bra's continuance on the earth, because it goes over 
a less portion of the disc, as is evident by the 
figure. 

The nearer the penumbra's centre is to the 
equator at the middle of the general eclipse, the 
longer is the duration of the eclipse at all those 
places where it is central, because, the nearer 
any place is to the equator the greater is the 
circle it describes by the earth's motion on its axis, 
and thus the place, moving quicker, keeps longer in 
the penumbra, whose motion is the same way with 
that of the place, though faster, as has been 
already mentioned. Thus (see the earth at D, and 
the penumbra at 12,) whilst the point b in the polar 
circle a b c d is carried from b to c by the earth's 
diurnal motion, the point don the tropic of cancer T 
is carried a much greater length from d to D; and, 
therefore, if the penumbra's centre goes one time 
over c and another time over D, the penumbra will 
be longer in passing over the moving place d than 



WONDERS OF THE HEAVENS. 



241 



I it was in passing over the moving place b. Con- 
sequently, central eclipses about the poles are of 
the shortest duration, and about the equator of the 
longest. 

In the middle of summer, the whole frigid zone 
included by the polar circle a h c d\s enlightened, 
and if it then happens that the penumbra's centre 
goes over the north pole, the sun will be eclipsed 
nearly the same number of digits at a as at c; but 
whilst the penumbra moves eastward over c, it 
moves westward over a, (because, with respect to 
the penumbra, the motions of a and c are contrary, 
for c moves the same way with the penumbra 
towards d, but a moves the contrary way towards 
b,) and, therefore, the eclipse will be of longer 
duration at c than at a. At a the eclipse begins 
on the sun's eastern limb, but at c on his western. 
At all places lying without the polar circles, the 
sun's eclipses begin on his western limb, or near 
it, and end on or near his eastern. At those 
places where the penumbra touches the earth, the 
eclipse begins with the rising sun, on the top of 
his western or uppermost edge ; and at those 
places where the penumbra leaves the earth, the 
eclipse ends with the setting sun, on the top of his 
eastern edge, which is then the uppermost, just at 
its disappearing in the horizon. 

That the moon can never be eclipsed but at the 
time of its being full, and the reason why it is not 
eclipsed at every full, has been shown already. In 
the figure on page 237 let S be the sun, E the 
earth, R R the earth's shadow, and B the moon in 
opposition to the sun. In this situation the earth 
intercepts the sun's light in its way to the moon, 
and when the moon touches the earth's shadow 
at V, it begins to be eclipsed on the eastern limb x, 
and continues eclipsed until the western limb y 
leaves the shadow at w. At B it is in the middle of 
the shadow, and consequently in the middle of the 
eclipse. 

The moon when totally eclipsed is not invisible 

if it be above the horizon, and the sky be clear ; 

but it appears generally of a dusky color, like 

tarnished copper, which some have thought to 

be the moon's native light. But the cause of its 

31 



being visible is the scattered beams of the sun, 
bent into the earth's shadow by going through 
the atmosphere, which, being more dense near 
the earth than at considerable heights above it, 
refracts or bends the sun's rays the more inward 
the nearer they pass to the earth's surface, than 
those rays which go through higher parts of the 
atmosphere, where it is less dense according to its 
height, until it becomes so thin or rare as to lose 
its refractive power. Let the circle fg h i, con- 
centric to the earth, include the atmosphere whose 
refractive power vanishes at the heights / and i, 
so that the rays Wfw and Y iv go on straight 
without suffering the least refraction. But all 
those rays which enter the atmosphere between 
/ and k, and between i and I, on opposite sides of 
the earth, are gradually more bent inward as they 
go through a greater portion of the atmosphere, 
until the rays W k and V / touching the earth at m 
and n are bent so much as ■ to meet at q, a little 
short of the moon, and therefore the dark shadow 
of the earth is contained in the space moqpn, 
where none of the sun's rays can enter. All the 
rest R R, being entered by the scattered rays which 
are refracted as above, is in some measure 
enlightened by these rays, and some of them 
falling on the moon, give it the color of tarnished 
copper, or of iron almost red hot. So that if the 
earth had no atmosphere the moon would be as 
invisible in total eclipses as it is when new. If 
the moon were so near the earth as to go into its 
dark shadow, suppose about p o, it would be 
invisible during its stay in it, but visible before 
and after in the fainter shadow R R. 

When the moon goes through the centre of the 
earth's shadow, it is directly opposite to the sun ; 
yet the moon has been often seen totally eclipsed 
in the horizon when the sun was also visible in the 
opposite part of it, for, the horizontal refraction 
being almost thirty-four minutes of a degree, and 
the diameter of the sun and moon being each at a 
mean state but thirty-two minutes, the refraction 
causes both luminaries to appear above the horizon 
when they are really below it. 

When the moon is full at twelve degrees from 



242 



WONDERS OF THE HEAVENS 



either of its nodes, it just touches the earth's 
shadow, but does not enter it. Let G H be the 




ecliptic, ef the moon's orbit where it is twelve 
degrees from the node at its full, c d its orbit 
where it is six degrees from the node, a b its orbit 
where it is full in the node, A B the earth's 
shadow, and M the moon. When the moon 
describes the line ef, it just touches the shadow, 
but does not enter into it ; when it describes the 
line c d, it is totally, though not centrally, 
immersed in the shadow; and when it describes 
the line a b, it passes by the node at M in the 
centre of the shadow, and takes the longest line 
possible, which is a diameter, through it, and 
such an eclipse being both total and central is of 
the longest duration, namely, three hours fifty- 
seven minutes six seconds from the beginning to 
the end if the moon be at its greatest distance 
from the earth, and three hours thirty-seven 
minutes twenty-six seconds if it be at its least 
distance. The reason of this difference is, that 
when the moon is farthest from the earth it moves 
slowest, and quickest when nearest to it. 

The moon's diameter, as well as the sun's, is 
supposed to be divided into twelve equal parts, 
called digits; and as many of these parts as are 
darkened by the earth's shadow, so many digits is 
the moon eclipsed. All the moon is said to be 
eclipsed above twelve digits, show how far the 
shadow of the earth is beyond the body of the moon 
on that edge to which she is nearest at the middle 
of the eclipse. 

It is difficult to observe exactly either the 



beginning or end of a lunar eclipse, even with a 
good telescope, because the earth's shadow is so 
faint, and ill defined about the edges, that, when the 
moon is either just touching or leaving it, the obscu- 
ration of her limb is scarcely sensible, and, there- 
fore, the nicest observers can hardly be certain to 
four or five seconds of time. But both the 
beginning and end of solar eclipses are visibly 
instantaneous, for the moment that the edge of the 
moon's disc touches the sun's his roundness seems 
a little broken on that part, and the moment the 
moon leaves the sun he appears perfectly round 



agam. 



In astronomy, eclipses of the moon are of great 
use for ascertaining the periods of its motions, 
especially such eclipses as are observed to be alike 
in all circumstances, and have long intervals of 
time between them. The longitudes of places are 
found by eclipses ; but for this purpose eclipses of 
the moon are more useful than those of the sun, 
because they are more frequently visible, and the 
same lunar eclipse is of equal extent and du- 
ration at all places where it is seen. Both solar 
and lunar eclipses serve to determine the time of 
any past event, for there are so many particulars 
observable in every eclipse, with respect to its 
quantity, the places where it is visible, (if of the 
sun,) and the time of the day or night, that it is 
impossible there can be two solar eclipses in the 
course of many ages which are alike in all circum- 
stances. 

From the above explanation of the doctrine of 
eclipses, it is evident that the darkness at our 
Savior's crucifixion was supernatural ; for he 
suffered on the day on which the passover was 
eaten by the Jews, on which day it was impossible 
that the moon's shadow could fall on the earth, 
as the Jews kept the passover at the time of full 
moon; nor does the darkness in total eclipses of the 
sun last above four minutes in any place, whereas 
the darkness at the crucifixion lasted three hours, 
and overspread at least all the land of Judea. 

OccuLTATioNS. The moon, in moving through 
its orbit, will appear to pass over such of the stars 
as lie in or near its apparent path. 



WONDERS OF THE HEAVENS 



243 



This phenomenon is called an occultation of the 
stars because they are entirely concealed from our 
view. Now the moon's apparent path through the 
heavens is constantly changing, owing to the 
inclination of its orbit to the ecliptic, and the 
continual motion of the line of the lunar nodes, so 
that all the stars situated within a certain zone, 
extending each side of the ecliptic, and of a 
breadth equal to double the greatest geocentric 
latitude of the moon, may suffer an occultation. 
The breadth of this zone on each side of the ecliptic 
is about thirteen degrees and twelve minutes, and 
those stars whose latitudes are less than six degrees 
and thirty-six minutes may suffer an occultation to 
some portion of the earth. 

To find the time when any of the stars situated 
in the above-mentioned zone will be occulted or 
eclipsed by the moon, we must find at what time 
the moon and star will be in conjunction, that is, 
at what time they will have the same longitude. 

If this conjunction happen at a time of the 
night when the star is visible, or within two hours 
of it, the occultation (other circumstances agreeing 
to render it one) will be visible. In order to find 
if the moon will pass above or below the star, or 
over it so as to produce an occultation, we must 
compute the moon's parallax in latitude, which, 
subtracted from its true latitude, if it be north, and 
added to it, if it be south, will give the apparent 
latitude of the moon as seen from the earth at the 
given place. Ifthe difference between the moon's 
apparent latitude, and the latitude of the star, does 
not exceed the semidiameter of the moon, the last 
will pass over the star and produce an occultation. 
When this difference exceeds the moon's semi- 
diameter, the latitude of the star being less than 
that of the moon, and the latitude of the moon 
being north, it will pass above the star — being 
south, it will pass below the star. When the star's 
latitude is greater than that of the moon, and the 
moon's latitude is north, it will pass below the 
star — if south, it will pass above the star. 

But the calculation of the moon's parallax in 
latitude is a tedious operation, and we may find, 
without the aid of this parallax, in some cases, if a 



conjunction will be attended with an occultation by 
the following rule : — If the difference between the 
latitude of the moon and that of the star exceeds 
one degree and thirty-seven minutes, no occulta- 
tion can take place; and if the difference be less 
than fifty-one minutes, there must be an occultation 
to some part of the earth. When the difference is 
between these limits, we must have recourse to the 
moon's parallax in latitude to ascertain if an occul- 
tation will happen. 

If it appears that an occultation will take place, 
we may find the longitude and latitude of the moon 
and of the star at the time of conjunction, the 
hourly motion of the moon in longitude and in 
latitude at the same time, its horizontal parallax 
and semidiameter, and the time when the star 
passes the meridian of the given place. With 
these elements we can proceed to project the 
occultations. 

In calculating an occultation of a planet, the 
same method will answer, with this difference only — 
Instead of the hourly motion of the moon in latitude 
and longitude, we must take the difference of the 
hourly motions of the moon and planet, if they are 
moving in the same direction, or their sum if they 
are moving in opposite directions, for the relative 
hourly motion. With this relative motion we may 
find the inclination of the relative orbit in the same 
manner as we should proceed in finding the angle 
of the moon's visible path with the ecliptic. 



SECTION II. 

Universal gravitation — Dr. Hooke's suggestions and experiments — 
Newton's successful investigation— All bodies tend toward each 
other — Pressure and weight the effects of gravity — Heavy and 
light, relative terms— Weight varies at different parts of the earth 
— How discovered — Gravity diminishes as we recede from the 
centre — There would be no weight if but one body existed — 
Gravity retains the moon in its orbit— Explanation— The planets 
affected by the same force— Nature of this force inexplicable- 
Attraction of mountains. 

The motions of the heavenly bodies have been 
variously accounted for. We have already advert- 
ed to the rude mechanism of deferent and epicyclic i 



244 



WONDERS OF THE HEAVENS. 



spheres, by which some of the ancient philosophers 
attempted to explain the celestial motions, as also 
to a more sensible attempt made by Cleanthes, 
another philosopher of Greece, who, from observing 
that bodies are easily carried round by whirlpools 
or vortices of water, imagined that the celestial 
spaces are filled with an ethereal fluid, which is in 
continual motion round the earth, and that it 
carried the sun and planets round with it. Though 
this hypothesis affords no real explanation of the 
phenomena, it was revived in modern times, and 
maintained by two of the most eminent mathema- 
ticians and philosophers in Europe, namely, by 
Des Cartes and Leibnitz, and for a long time met 
with general acquiescence. But a much nearer 
approximation to right conceptions on this subject 
was made by many philosophers of modern times, 
who supposed that the planets were deflected from 
uniform rectilineal motions by forces similar to 
what we observe in the motions of magnetical and 
electrical bodies, or in the motion of common heavy 
bodies, where one body seems to influence the 
motion of another at a distance from it without any 
intervening impulsion. Fermat was the first who 
suggested that the weight of a body is the sum of 
the tendencies of each particle of matter in the 
body to every particle of the earth. Kepler made 
another approximation to the truth, when he said 
that if there were two bodies placed out of the 
reach of all external forces, and at perfect liberty 
to move, they would approach each other with 
velocities inversely proportional to their quantities 
of matter ; when he asserted that the earth and the 
moon mutually attract each other, and are pre- 
vented from meeting by their revolution round 
their common centre of attraction ; and when he 
attributed the tides to the attractive influence of 
the moon in heaping up the waters immediately 
under it. 

But Dr. Hooke formed the most precise theory on 
this subject. At a meeting of the Royal Society, 
May 3d, 1668, he expressed himself in the follow- 
ing manner:- — "I will explain a system of the 
world very different from any yet received, which 
is founded on the three following propositions : — 



" That all the heavenly bodies have not only a 
gravitation of their parts to their own centres, but 
they mutually attract each other. 

" That all bodies having a simple motion will 
continue to move in straight lines, unless con- 
tinually deflected from them by some extraneous 
force. 

"And that this attraction is greater in proportion 
to the proximity of the bodies." 

The philosophical views stated in the above 
propositions relative to the celestial motions, were 
illustrated by an experiment which Dr. Hooke 
exhibited to the society. A ball, suspended by a 
long thread from the ceiling, was made to swing 
round another ball laid on a table immediately 
below the point of suspension. When the impulse 
given to the pendulum was nicely adjusted to its 
deviation from the perpendicular, it described a 
perfect circle round the ball on the table ; but 
when the impulse was very great or very little, it 
described an ellipse having the other ball in its 
centre. The force under the influence of which 
this circular or elliptic motion was produced, 
Hooke showed to be a deflecting force, proportional 
to the distance from the other ball. But he added 
that though this illustrated the planetary motions 
in some degree, yet it was not wholly suitable to 
their case, for the planets describe ellipses, having 
the sun not in their centre, but in their focus, so 
that they are not retained in their orbits by a force 
proportional to the distance from the sun. 

Thus we see that certain points of resemblance 
between the motions of the planets and the motions 
of magnets and heavy bodies had attracted the 
attention of many philosophers ; but these observers 
failed to deduce any satisfactory conclusions from 
the principles they thus dimly discerned. 

At length the powerful genius of Newton was 
directed to the subject, and, by his penetrating 
sagacity, the law of universal gravitation was 
brought fully into view, and successfully applied to 
explain the celestial phenomena. 

About the year 1666, the twenty-fourth year of 
his age, Newton, having retired into the country, 
in order to avoid the plague, which raged at that 



WONDERS OF THE HEAVENS 



245 



time with great violence, was there led, by the 
leisure such a situation afforded him, to meditate 
on the probable cause of the planetary motions, and 
upon the nature of the central force by which they 
are retained in their orbits. In this inquiry the 
phenomena of falling bodies first engaged his 
attention, and, pursuing the ideas which a careful 
consideration of the subject presented to his mind, 
he carried his researches from the earth to the 
heavens, and began to investigate the nature of 
motion in general. Because there is motion, he 
observed, there must be a force which produces it: 
but what is this force ? That a body, when left to 
itself, will fall to the ground, is known to the most 
ignorant; but if you ask them the reason of its 
doing so, they will consider you a fool or a mad- 
man. The circumstance is too common to excite 
their surprise, although philosophers are so much 
embarrassed with it that they find it almost inex- 
plicable. 

Let us follow Newton, and examine this question 
a little farther. Does the cause of weight or 
gravity exist in the bodies themselves, or out of 
them? It seems natural to conclude that the 
propensity which all suspended bodies have of 
falling to the earth, exists in the bodies themselves. 
When we take a stone and let it drop from the 
hand it falls immediately to the ground, and it would 
fall farther if there were a hole in the earth, and 
nothing impeded its progress. 

The same happens to all other bodies with which 
we are acquainted. There is no material substance, 
either great or small, which will not fall toward the 
earth the moment it is disengaged and free from all 
outward impediments. 

In like manner it may be observed that when a 
stone, or any other body, is placed upon a table, it 
presses the table with the same force by which it 
would, if left to itself, fall to the ground ; and if a 
body be suspended at the end of a string, the force 
that pushes it downwards stretches the string, and, 
if it is not sufficiently strong, will break it. From 
these circumstances it appears plain that all 
bodies press with a certain force against the 
obstacles which support and hinder them from 



falling, and that the degree of force, in either case, 
is precisely the same as that, which, in free space, 
would bring them to the ground. 

The cause of this propensity in all bodies to fall 
to the earth, be it what it may, is called gravita- 
tion or attraction ; and when a substance is said to 
be very heavy, nothing more is meant than the 
great tendency it has to fall to the ground, or the 
great force with which it presses upon any other 
body that supports it. The weight and gravity 
of a body may therefore be considered as the same 
thing. Each of them expresses the force by which 
the body is impelled toward the earth, whether 
this force exist in the body itself, or out of it. 

With this property of bodies, obvious as it is, the 
ancients were very imperfectly acquainted. They 
believed that there were substances, such as 
vapors and smoke, that, by their nature, were light, 
and would, for that reason, ascend. This notion, 
however, as well as that of absolute levity in 
general, is now known to be erroneous, for, in a 
receiver perfectly exhausted, or a space void of 
air, all bodies whatever, smoke or stone, gold or 
feathers, would fall in the same time. The distinc- 
tion, therefore, between light and heavy bodies is 
merely relative, as they are of the same nature, 
and have all a like propensity to fall toward the 
earth. 

Neither can there be the least doubt that gravity 
acts as a force, for whatever is capable of putting 
a body in motion is properly so called. But in 
all forces there are two things to be considered — 
the direction in which they act, and their intensity 
or power. With respect to the direction of gravity, 
we are sufficiently assured, both by reason and 
experience, that a body in falling moves towards a 
point which is in, or near, the centre of the earth, 
or rather in a straight line that is perpendicular 
to its surface. The intensity or power of gravity 
is proportional to the weight of the body under 
consideration, those that are the heaviest, or 
that weigh the most, being always observed to 
descend with the greatest force, and those that 
weigh the least, with the least force ; so that the 
weight of every body may always be considered as 



246 



WONDERS OF THE HEAVENS 



the just measure of its gravity, or of the force by 
which it is made to fall toward the earth. 

The weight of a body, as we have before stated, 
is less at the equator than at either pole ; and in 
every other situation it varies in a certain propor- 
tion according to the latitude of the place, which is 
occasioned by the oblate spheroidal figure of the 
earth. This difference, however, is not discovera- 
ble by means of a balance, or the scales which are 
usually employed upon these occasions, because 
the Aveight against which the body is opposed is 
subject to the same variation. The method by 
which it has been determined is by observations 
made on the vibrations of pendulums of equal 
length, which have been found to move swifter as 
they are more distant from the equator. 

It may be farther observed, that, since the earth 
is a globe, or nearly, and gravity acts perpetually 
in straight lines that are perpendicular to its 
surface, if a hole should be bored from one side to 
the other entirely through it, and a body were 
placed at the centre, it would remain there forever 
unsupported, and be wholly without weight, 
because, in this situation, being equally acted upon 
on all sides by the same attractive force, it could 
have no tendency to move either way, and conse- 
quently would continue at rest. For the same 
reason, if a body were dropped into this orifice 
from the earth's surface, the velocity acquired at 
the centre by the repeated impulses of gravity 
during the time of its fall would carry it on to the 
opposite extremity of the opening, from which it 
would again return, and, provided the medium had 
no resisting power, would perpetually continue to 
move backward and forward. 

If we extend our researches, we shall find as 
we recede from the earth's surface a diminution 
of the force of gravity, the cause of which is not 
obvious. All that can be said, indeed, on this 
head is, that the fact has been ascertained from 
constant observations, but the cause of it is as little 
understood as that of gravity itself. The truth of 
facts, however, is not weakened from the causes 
being unknown ; and Newton proved, in a satis- 
factory manner, that the gravity of bodies above 



the earth's surface continually diminishes as the 
squares of their distances from the centre increase, 
or, which is the same, that the forces are as four to 
one when the distances from the centre are as one 
to two, as nine to one when the distances are as 
one to three, and so on. 

From this account, it will be perceived that 
gravity is a force which acts upon all bodies, 
whether at rest or in motion, and gives them a 
tendency to fall toward the centre of the earth, 
and that this force, whatever it may be, acts most 
strongly upon bodies nearest the earth's surface. 
Does it appear, then, that gravity or weight is an 
inherent and necessary property of body? It 
increases or diminishes perpetually, according to a 
certain proportion of the distance from the centre ; 
but what is permanent does not admit of such 
mutations. If there were but one body in the 
universe, we could by no reasonable supposition 
consider it as possessing weight. 

Newton perceived that the force of gravity was 
not confined to the surface of our globe, being 
found to act in the same manner at the greatest 
heights to which we can ascend ; and he therefore 
conceived that it might extend, under some modifi- 
cations, as far as the moon, and be the means of 
retaining it in its orbit, by causing a constant 
deflection from a rectilinear path. 

The conjecture was as ingenious as it was 
simple; but before it could be submitted to the 
test of calculation, it was necessary to assume 
some hypothesis relative to the strength or energy 
of this force with respect to the distance. In this 
case, the supposition made was, that the power of 
gravity, as above mentioned, decreases as the 
square of the distance increases, — to which idea he 
was probably led by knowing that light, heat, and 
other emanations thrown off" from certain bodies, 
become weaker in this proportion as they proceed. 

But when Newton first attempted to verify this 
conjecture, the requisite data with regard to the 
distance of the moon in radii of the earth, and the 
measure of the earth's radius, were but imperfectly 
known, and the result he obtained, though near 
the truth, was not so exact as could be wished. 



WONDERS OF THE HEAVENS 



247 



He therefore, at first, abandoned his hypothesis, 
which may be regarded as a remarkable proof of 
the cool and dispassionate frame of mind that 
this great man preserved, even at the time when 
he had flattered himself with having discovered one 
of the most important secrets of nature. 

A few years afterwards, he was induced to return 
to his calculations in consequence of more correct 
data having been obtained in the interval by the 
measure of an arc of the meridian. In this second 
attempt Newton was completely successful. It is 
related, that, toward the conclusion of his computa- 
tion, he became so agitated that he was obliged 
to request a friend to assist him in finishing it ; 
and certainly a moment of greater importance will 
never be recorded in the annals of science. 

* If a particle of matter be subjected, at the same time, to the action 
of two moving forces, each of which would separately cause it to 
det;cribe the side of a parallelogram in a given time, the particle will 
describe the diagonal in the same time. We shall not be expected to 
enter at any considerable length into the doctrines of physical astron- 
omy. This subject requires for its full discussion ample space, and 
all the resources of the higher mathematics. The mere elements of 
geometry, however, are sufficient to indicate generally some of the 
fundamental principles. Let us suppose that S is a fixed point, and 
that a body moves in the direction AB, with an uniform velocity, at 




such a rate, that, if not disturbed by any external cause, it would move 
from B to 5 in a 'second of time. Let us also suppose, that, when the 
body arrives at B, it receives an impulse in the direction B S, and of 
such intensity, that, if acting alone, it would cause the body to move 
uniformly from B to H in a second. Complete the parallelogram 
H B J C, and draw the diagonal B C : the impulse at B, combined with 
the tendency to continue its motion in the line B h, will cause the body 
to move along the diagonal B C, so that, at the end of a second, it will 
actually be at the point C, and, if no external cause acted on the body, 
by the first law it would continue to move uniformly ever after in 
the direction B C c, so that, in the next second, it would describe a line 
Cc, equal to B C. But now suppose that the body, when at C, re- 
ceives a second impulse in the direction C S, by which it would be 
carried uniformly from C to I in a second; then, completing the 



But, leaving these observations for the present, 
let us now see in what way this doctrine is applica- 
ble to the subject in question. For this purpose, 
imagine the moon, at the first moment of its 
creation, to have been projected forward with a 
certain velocity in a right-lined direction ; then 
as soon as it began to move, gravity would operate 
and impel it towards the centre of the earth. 
But, as a body impelled by two forces will follow 
the direction of neither, the moon, so circum- 
stanced, would neither proceed directly forward, 
nor fall directly downward, but, keeping a middle 
course, would move round the earth in a curvi- 
linear orbit.* 

This idea will be more fully illustrated by 
attending to the motion of a ball, or other projec- 

parallelogram D I C c, the actual path of the body will be the diagonal 
CD, which will be uniformly described in a second ; and, if undis- 
turbed, the motion would be continued uniformly in the straight line 
CDrf, the distance Drf described in the next second being equal to 
C D. A third impulse at D in the direction D S, such as would 
carry the body uniformly from D to K in a second of time, would, 
when combined with the tendency to move in the direction D d, pro- 
duce a motion along D E, the diagonal of the parallelogram E K D f/, 
and a fourth impulse in the direction E S, would, when combined 
with the motion in the direction E e, produce a motion along the 
diagonal E F, and so on. In this way, by successive instantaneous 
impulses, a body may be made to describe the path A B C D E F, &c., 
which will be all in one plane. 

Since the lines A B, B 5 are equal, the triangles A S B, B S 5 are 
equal ; but, because C J is parallel to S B, the triangle B S S is equal 
to the triangle B S C, therefore the triangle B S C is equal to A S B. 
In like manner, it may be proved that C S D is equal to B S C, and 
D S E to C S D, and so on. Thus it appears that the triangles A S B, 
B S C,C SD, D S E, &c., are all equal. If we suppose a straight line 
to be drawn from the moving body to the fixed point S, and to be 
continually carried along with it, it is evident that this line will pass 
over or generate the equal areas A S B, B S C, C S D, D S E, &c., in 
equal intervals of time. It is also evident that the shorter the interval 
between the impulses communicated to the moving body, the greater 
will be the number of sides of the figure formed by the diagonals of 
the parallelograms, and the nearer will the line composed of these 
diagonals approach to a curve. If we suppose, therefore, that the 
body is urged towards F by a force acting, not at intervals, but ■ 
incessantly, the body will move in that curve to which, as its limit, 
the line composed of the diagonals continually approaches, while the 
line drawn from the moving body A S, or radius vector, will continue 
to describe areas proportional to the times. 

From the important conclusion to which we have now been led, 
we may infer, conversely, that, if a body revolve in a curvilinear path 
about a point, and if the radius vector drawn from that point describe 
round it areas proportional to the times, the body is deflected from 
the rectilineal path by a force directed to that point. Now this is 
exactly the case of the planets, both primary and secondary. The 



248 



WONDERS OF THE HEAVENS 



tile. A ball discharged from a cannon in a hori- 
zontal direction, does not fall to the ground till it 
has proceeded a considerable distance ; and if it be 
projected from the top of a mountain, or other 
eminence, it will fly still farther before it comes to 
the earth. Increase the force, and the distance will 
be augmented accordingly. And thus, in imagina- 
tion at least, we can suppose the ball to be dis- 
charged with such a velocity that it will circulate 
continually round the earth in the manner of a 
moon. 

Newton did not content himself with stopping 
here, but began to generalize the problem, and, by 
means of mathematics, soon came to this important 
conclusion, that a body which moves in a curve 
round a fixed point, by virtue of a force directed to 
that point, describes equal areas in equal times. 
This is a law of nature which had been before dis- 
covered by Kepler from observation. The suppo- 
sition, therefore, that the moon is under the 
influence of such a force, is confirmed both by 
science and experience; and every improvement 
that has since been made in the theory of its 
motion has been derived from these principles. 

Gallileo had before discovered, that, on the 
supposition of gravity's acting in parallel lines, a 
body, projected with any force whatever, would 
describe a parabola if the medium had no resist- 
ance. But Newton extended this problem, and 
made it more general. He no longer considered 
the falling body as having a limited distance, nor 
the force of gravity as acting in parallel lines, but 
regarded the centre of the earth as the centre of 
attraction, and, taking into consideration the uniform 
lateral velocity of the projectile, he proved that it 
would move round the earth in an elliptical orbit, 
having the centre of the earth in one of its foci. 
Whence the projectile may be considered as a 

former describe curvilinear orbits round the sun, and, according to 
the second of Kepler's laws, the radius vector describes areas propor- 
tional to the times. Hence we may infer that each is retained in its 
orbit by a centripetal force, directed towards the sun, and that this 
force is counteracted by a centrifugal force, generated by the planet's 
motion in its orbit. In like manner, each secondary planet revolves 
about its primary, the areas described by the radius vector following 
the same law, so that the secondary must be acted upon by a cen- 
tripetal force directed towards the primary planet. 



moon, moving round the earth, or as one of the 
satellites of Jupiter, Saturn, or Herschel, moving 
round those planets, the circumstances in either 
case being the same. 

From the data above mentioned it was also easy 
to show that the moon is acted upon by gravity 
according to the law there stated, for the diameter 
of the earth in feet, and the mean distance of the 
moon in radii of the earth, being known, as well as 
the time of one lunar revolution, the circumference 
of the lunar orbit, and the measure of the arc which 
the moon describes in a given time, could be readily 
determined, and thence the versed sine of that arc, 
or the deflection from a tangent to the orbit at any 
point of the curve, which by calculation was found 
to be about 16tV feet in a minute, or sixty seconds 
of time. So that, if the moon were deprived of the 
impulse by which it has a tendency to move in a 
right line from west to east, and the central force 
only remained, it would fall toward our globe, and 
describe the above-mentioned space in the first 
minute of its descent. 

This being ascertained, Newton compared the 
space which would thus be described by the moon 
at its present distance, with that which it would 
have described in the same time if placed near the 
earth's surface, and found that, in the latter case, 
the space fallen through in one minute would be 
the square of 60 multiplied by 16 tV feet. Then, 
comparing the distance of the centre of the earth 
from the surface, or the radius of the earth with 
the distance of the moon from the same centre, 
which was known to be equal to 60 of those radii, 
he found that the force of gravity at the earth's 
surface was to its force at the distance of the 
moon as the square of 60 to 1, so that the force 
decreases as the square of the distance increases. 
In a similar manner, he found that the same law 
obtained with respect to the other planets, from 
which he concluded that they must be acted upon 
by gravity in a similar manner, and that the whole 
universe is governed by the same laws, it being 
evident that so exact a conformity, or rather such 
a perfect identity of effects, can only arise from 
an identity of causes. 



WONDERS OF THE HEAVENS 



249 



These discoveries are, like the genius of their 
author, universal. But, before we proceed any 
farther, it will be proper to inquire a little into the 
nature of gravitation in general, that powerful 
agent which produces so many astonishing effects. 
It has been shown, that, by the action of this invisi- 
ble power, a stone is made to fall to the ground, 
the moon to circulate about the earth, and the 
satellites of the other planets to revolve about their 
respective primaries. The Newtonian doctrine 
which proves the truth of these laws from mathe- 
matical principles, is called "the system of universal 
gravitation or attraction." But what is this occult 
principle of sympathy and union which gives life 
and motion to inanimate beings, and how does it 
act ? The effects are visible, but the agent is hidden 
from our senses. It eluded the search of Newton. 
He who soared to the utmost regions of space, and 
looked through nature with an eagle eye, was 
unable to discover it. 

That there is, however, such a principle is 
beyond a doubt. To deny its existence would be 
to deny the truth of facts, established both by 
experiment and demonstration. That two distant 
bodies will approach each other without any 
visible agent either drawing or impelling them, 
may be made manifest by various instances. The 
loadstone and a piece of iron mutually attract each 
other; and in electricity we have numberless 
experiments to show that bodies of various kinds 
have a like tendency to approach and adhere to 
each other. These bodies, it is true, act by par- 
ticular laws, different from that of gravity; but 
they serve sufficiently well to illustrate the nature 
of that principle. 

Lest these instances should be thought insuffi- 
cient, it may be well to mention another, which, 
independently of mathematical demonstration, goes 
to show the universality of this property. Thus, 
according to the Newtonian theory, the principle 
of attraction pervades the minutest particles of 
matter, and the combined action of all the parts of 
the earth forms the attraction of the whole. 
Hence, for the same reason that a heavy body 

tends downwards in a perpendicular to the earth's 

32 



surface, it must be attracted more or less toward 
the centre of any neighboring mountain according 
to the quantity of matter contained in it, and the 
effect of this attraction, or the accelerative force 
produced by it, must depend on the distance of the 
mountain from the gravitating body, because this 
force decreases as the square of the distance 
increases. Upon these principles, then, the plumb- 
line of a quadrant, or any other astronomical instru- 
ment, must be deflected from its proper situation 
by a small quantity towards the mountain, and 
the apparent altitudes of the stars taken with such 
an instrument must be altered accordingly, that is, 
if the zenith distance of a star were observed at 
two stations under the same meridian, one on the 
south side of the mountain and the other on the 
north, the star, on account of the plumb-line being 
attracted out of its vertical direction, must appear 
too much to the north by the observation at the 
southern station, and too much to the south by 
that at the northern station, and consequently the 
difference of the latitudes of the two stations 
resulting from these observations would be greater 
than it really is. 

If, then, the true difference of the latitudes of the 
two stations be determined by means of a series of 
triangles, the excess of the difference found by the 
observations on the star above that found by the 
measurement will be the effect produced by the 
attraction of the mountain, and the half of it will 
be the effect of such attraction on the plumb-line of 
the instrument at each observation, provided the 
mountain attracts equally on both sides. The first 
idea of determining the quantity of this attraction 
was suggested by Newton ; but nothing was done 
until Bouguer and La Condamine were employed, 
in 1738, in measuring an arc of a meridian near 
Quito, in Peru, when they thought they perceived 
a deflection in the plumb-line of their instrument 
from the effect of the attraction of Chimborazo, the 
highest mountain of the Andes, which, by a rough 
computation, founded upon a few observations 
similar to those above mentioned, they supposed 
to be equal to about the two thousandth part of the 
attraction of the whole earth. They, however, 



250 



WONDERS OF THE HEAVENS 



had neither the means nor the leisure to prosecute 
the inquiry, and nothing more was attempted till 
Maskelyne made a proposal to the Royal Society 
for this purpose, in 1772, in consequence of which 
he was deputed, in 1774, to make the trial, accom- 
panied with proper assistants, and furnished with 
the most accurate instruments. The mountain 
selected by him for the scene of his operations was 
Schehallien, in Scotland, the direction of which is 
nearly east and west, its mean height above the 
surrounding valley about two thousand feet, and 
its highest part above the level of the sea three 
thousand five hundred and fifty feet. Two stations 
for observation were selected, one on the north 
and the other on the south side of the mountain, 
and every circumstance that could contribute to the 
accuracy of the experiment was regarded. From 
the observation of ten stars near the zenith, com- 
pared with a measurement by triangles formed 
from two bases on different sides of the mountain, 
it was found, in the way above stated, that the 
force of attraction drew the plumb-line of the 
instrument about six seconds out of its vertical 
direction. 

This instance is sufficient to show that all bodies 
attract and are attracted; and it has been farther 
proved, by Newton, that their mutual actions upon 
each other are in exact proportion to the quantity 
of matter they contain. 

"When we consider," says an ingenious writer, 
" that, according to the doctrine of Newton, every 
single satellite of Saturn must gravitate toward the 
other six, the other six toward the seventh, all the 
seven toward Saturn, and Saturn with all of them 
toward the sun, according to a particular law, what 
skill in geometry must have been requisite to 
unravel the intricacies of so many different rela- 
tions! It was a daring attempt to undertake it, 
and one cannot perceive, without astonishment, 
that, from so abstract a theory, formed of so many 
particular theories, and each of them perplexed 
with innumerable difficulties, conclusions should 
always arise exactly conformable to fact and 
experience." 



SECTION III. 

Tides— Kepler's fanciful theory— Newton's theory— General course 
of the tides — Owing principally to the moon's attraction— In part 
to the sun's— Farther explanation of the tides— Cause of spring and 
neap tides— Priming and lagging of the tides— Declination of the 
sun and moon affect the tides— Establishment of a port— Excep- 
tions to the general laws — Mediterranean and Baltic seas — Times 
of high water different in neighboring ports — Theory of Mr. Red- 
field. 

Let us now descend into the world of waters. 
By what power or cause is it that this vast liquid 
body rises and falls alternately twice a day in a 
manner so constant and regular? The ancients 
considered it as one of the greatest mysteries of 
nature, and were utterly at a loss to account for it. 
Aristotle is represented as having thrown him- 
self into the sea because he was unable to explain 
its motions ; and it is said, that, when he was in 
India, he wished to follow the tide in its ebb to see 
where it would go. 

Kepler, in one of his reveries, considered the 
earth as a living being, and the ebb and flow of the 
sea as its respiration. He fancied that men and 
other creatures were insects which fed upon this 
animal, bushes and trees the bristles on its back, 
and the waters of the seas and rivers a liquid cir- 
culating in its veins. Kepler, however, afterward 
adopted a more philosophical theory, which he thus 
explains in his " Physics of the Heavens." " The 
orb of the attracting power which is in the moon 
extends as far as the earth, and draws the waters 
under the torrid zone, acting upon places where it 
is vertical, insensibly on confined seas and bays, 
but sensibly on the ocean, whose beds are large, 
and in which the waters have the liberty of recip- 
rocation, that is, of rising and falling." And in his 
Lunar Astronomy he says, "The cause of the tides 
in the sea appears to be the bodies of the sun and 
moon drawing the waters." This hint being given, 
Newton improved upon it, and wrote so amply on 
the subject as to make the theory in a manner his 
own, and discovered the cause of their rising on 
the side of the earth opposite the moon. Kepler 
believed that the presence of the moon occasioned 
an impulse that caused another in her absence. 

The ocean, it is well known, covers a large part 



WONDERS OF THE HEAVENS 



251 



of the globe, and the body of water is in continual 
motion, ebbing and flowing without intermission. 
What connection these motions have with the moon 
we shall see as we proceed. But at present it will 
be sufficient to observe that they always follow a 
certain general rule. For instance, if the tide be 
now at high-water mark in any port or harbor 
which lies open to the ocean, it will presently sub- 
side and flow regularly back for about six hours, 
when it will be found at low-water mark ; after 
this it will again gradually advance for six hours, 
and then return back in the same time to its former 
situation, rising and falling alternately twice a 
day, or in the space of about twenty-four hours. 

The interval between the flux and reflux is, how- 
ever, not precisely six hours, but about eleven 
minutes more; so that the time of high water does 
not always happen at the same hour, but is about 
three quarters of an hour later every day for thirty 
days, when it again recurs as before. For example, 
if it be high water to-day at noon, it will be low 
water at eleven minutes past six in the evening, 
and consequently, after two changes more, the time 
of high water to-morrow will be about three quar- 
ters of an hour after noon ; the day following it 
will be at about half an hour after one, the day 
after at quarter past two, and so on for thirty days, 
when it will again be high water at noon, the same 
as on the day the observation was first made, which 
answers to the motion of the moon ; for that planet 
rises every day about three quarters of an horn- 
later than upon the preceding, and, by moving in 
this manner round the earth, completes her revolu- 
tion in about thirty days, and then begins to rise 
about the same time as before. 

To make the matter plainer, suppose, that, at a 
certain place, it is high water at three o'clock in 
the afternoon upon the day of new moon; the 
following day it will be high water at three quarters 
of an hour after three, the day after at half past 
four, and so on till the next new moon, when it will 
again be high water at three o'clock as before. 
And, by observing the tides continually at the 
same place, they will always be found to follow the 
same rule, the time of high water upon the day of 



every new moon being nearly at the same hour, 
and three quarters of an hour later every succeed- 
ing day. ' 

Such a perfect harmony of motions as is here 
pointed out could not possibly arise from the mere 
concurrence of accidental causes, or the uncertain 
operations of blind chance. They are in such 
exact conformity with the motions of the moon, 
that, independently of all mathematical considera- 
tions, we should be induced to look to that planet 
as their cause. Neglecting, therefore, for the 
present, all such exceptions as do not affect the 
truth of the theory, we will proceed to show that 
these phenomena are principally occasioned by the 
moon's attraction. 

That the moon by her attraction should heap up 
the waters under her, seems to most persons very 
natural : that the same cause should, at the same 
time, heap them up on the opposite side of the 
earth, seems to many palpably absurd. Yet nothing 
is more evident when we consider that it is not by 
her whole attraction, but by the difference of her 
attractions at the two surfaces and at the centre, 
that the water is raised. A drop of water existing 
alone would take a spherical form by reason of the 
attraction of its parts ; and if the same drop were 
to fall freely in a vacuum under the influence of an 
uniform gravity, since every part would be equally 
accelerated, the particles would retain their relative 
positions, and the spherical form be unchanged. But 
suppose it to fall under the influence of an attraction 
acting on each of its particles independently, and 
increasing in intensity at every step of the descent ; 
then the parts nearer the attracting body would be 
attracted more than the central, and the central 
than the more remote parts, and the whole would 
be drawn out, in the direction of the motion, into 
an oblong form, the tendency to separation being, 
however, counteracted by the attraction of the 
particles on each other, and a form of equilibrium 
being thus established. Now, in fact, the earth is 
constantly falling to the moon, being continually 
drawn by it out of its path, the nearer parts more 
and the remoter less than the central parts; and thus, 
at every instant, the moon's attraction acts to force 



252 



WONDERS OF THE HEAVENS 



down the water on the sides at right angles to her 
direction, and raise it at the two ends of the 
diameter pointing towards her. Geometry corrob- 
orates this view of the subject, and demonstrates 
that the form of equilibrium assumed by a layer of 
water covering a sphere under the influence of the 
moon's attraction would be an oblong ellipsoid, 
having the semiaxis directed towards the moon 
longer by about fifty-eight inches than that trans- 
verse to it. 

There is never time, however, for this spheroid 
to be fully formed. Before the waters can take 
their level the moon has advanced in her orbit, 
both diurnal and monthly, (for, in this theory, it will 
answer the purpose of clearness better if we suppose 
the earth's diurnal motion transferred to the sun 
and moon in the contrary direction,) the vertex of 
the spheroid has shifted on the earth's surface, and 
the ocean has to seek a new bearing. The effect 
is to produce an immensely broad and excessively 
flat wave, (not a circulating current,) which follows, 
or endeavors to follow, the apparent motions of the 
moon, and must, in fact, if the principle of forced 
vibrations be true, imitate all the periodical ine- 
qualities of that motion. When the higher or 
lower parts of this wave strike our coasts, they 
experience what we call high and low water. It 
will be convenient, as adding much to the simplici- 
ty of the subject, to consider the earth as a perfect 
sphere, wholly covered with an ocean of uniform 
density ; then, as it is the peculiar nature of fluids 
to communicate in all directions the impressions 
they receive, it is manifest that the action of terres- 
trial gravit}^ would cause the sea to become every- 
where of the same depth, or to have its waters level 
throughout the whole extent of its globe ; and as 
neither the diurnal rotation of the earth, nor its 
projectile motion, which act equally on all its parti- 
cles, would cause any disturbance in this state of 
equilibrium, reason teaches us that it is to the 
action of some external force we are to look for the 
cause of the tides, and a little attention to the 
nature of the moon's attraction will convince us that 
we are right in ascribing the agency principally to 
that body. 



The power of gravity, as we have stated in the 
preceding section, diminishes as the square of the 
distance increases, and therefore the waters at Z 




on the side of the earth ABCDEFGH next the 
moon M are more attracted than the central parts 
of the earth by the moon, and the central parts 
are more attracted by her than the waters on the 
opposite side of the earth at n, and therefore the 
distance between the earth's centre and the waters 
on its surface under and opposite to the moon will 
be increased. For, let there be three bodies at 
H^ 0,. and D : if they are all equally attracted by 
the body M, they will all move equally fast toward 
it, their mutual distances from each other continu- 
ing the same; if the attraction of M is unequal, 
then that body which is most strongly attracted 
will move fastest, and this Mali increase its distance 
from the other body. Therefore, by the law of 
gravitation, M will attract H more strongly than it 
does 0, by which the distance between H and 
will be increased, and a spectator on will per- 
ceive H rising higher toward Z. In like manner, 
being more strongly attracted than D, it will 
move farther towards M than D does ; consequently 
the distance between and D will be increased, 
and a spectator on 0, not perceiving his own 
motion, will see D receding farther fi:-om him 
towards n, all effects and appearances being the 
same, whether D recedes from 0, or from D. 

Suppose, now, there is a number of bodies, as 
A,B, C,D, E, F, G, H placed round 0, so as to 
form a flexible or fluid ring; then, as the whole is 
attracted towards M, the parts at H and D will 



WONDERS OF THE HEAVENS. 



253 



have their distance from increased, whilst the 
parts at B and F, being nearly at the same dis- 
tance from M as is, will not recede from one 
another, but rather, by the oblique attraction of 
M, they will approach nearer to 0. Hence, the 
fluid ring will form itself into an ellipse Z I B L ra 
K F N Z, whose longer axis nOZ produced will 
pass through M, and its shorter axis B F will 
terminate in B and F. Let the ring be filled with 
bodies so as to form a fluid sphere round ; then, 
as the whole moves toward M, the fluid sphere 
being lengthened at Z and n, will assume an oblong 
or oval form. If M is the moon, the earth's 
centre, A BCDEFGH the sea covering the 
earth's surface, it is evident, by the above reason- 
ing, that, whilst the earth by its gravity falls toward 
the moon, the water directly below her at Z will 
swell and rise gradually towards her, also the 
water at D will recede from the centre, (strictly 
speaking, the centre recedes from D,) and rise on 
the opposite side of the earth, whilst the water at B 
and F is depressed, and falls below the former 
level. Hence, as the earth turns round its axis 
from the moon to the moon again in twenty-four 



hours and three quarters, there will be two tides of 
flood and two of ebb in that time, as we find by 
experience. 

As this explanation of the ebbing and flowing of 
the sea is deduced from the earth's constantly fall- 
ing toward the moon by the power of gravity, some 
may find a difficulty in conceiving how this is 
possible when the moon is full, or in opposition to 
the sun, since the earth revolves about the sun, 
and must continually fall towards it, and there- 
fore cannot fall contrary ways at the same time ; or 
if the earth is constantly falling towards the moon, 
they must come together at last. To remove this 
difficulty, let it be considered that it is not the 
centre of the earth that describes the annual orbit 
round the sun, but the common centre * of gravity 
of the earth and moon together, and that, whilst the 
earth is moving round the sun, it also describes a 
circle round that centre of gravity, going as many 
times round it in one revolution about the sun as 
there are lunations or courses of the moon round 
the earth in a year, and therefore the earth is 
constantly falling towards the moon from a tangent 
to the circle it describes round the said common 




centre of gravity. Let M be the moon, T W part 
of the moon's orbit, and C the centre of gravity of 
the earth and moon. Whilst the moon goes round 
her orbit, the centre of the earth describes the 
circle g ed round C. To this circle g ak is a 
tangent ; and therefore, when the moon has gone 
from M to a point but little beyond W, the earth 
has moved from g to e, and in that time has fallen 
towards the moon from the tangent at a to e, and 
so round the whole circle. 



The sun's influence in raising the tides is but 
small in comparison to the moon's, for though the 
earth's diameter bears a considerable proportion to 
its distance from the moon, it is next to nothing 

* This centre is as much nearer the earth's centre than the moon's 
as the earth is heavier, or contains a greater quantity of matter than 
the moon, namely, about forty times. If both bodies were suspended 
on It, they would hang in equilibrium. So that dividing the moon's 
distance from the earth's centre by the excess of the earth's weight 
above the moon's, the quotient will be the distance of the common 
centre of gravity of the earth and moon from the earth's centre. 



254 



WONDERS OF THE HEAVENS 



when compared with the distance of the sun ; and 
therefore the difference of the sun's attraction on 
the sides of the earth under and opposite to him is 
much less than the difference of the moon's attrac- 
tion on the sides of the earth under and opposite to 
her, and consequently the moon must raise the tides 
much higher than they can be raised by the sun. 

On this theory, so far as we have explained it, 
the tides ought to be highest directly under and 
opposite to the moon, that is, when the moon is 
due north and south. But we find, that, in open 
seas, where the water flows freely, the moon M is 
generally past the north and south meridian, as atp, 
(last figure but one,) when it is high water at Z and 
at n. The reason is obvious, for though the moon's 
attraction was to cease altogether when she was 
past the meridian, yet the motion of ascent com- 
municated to the water before that time would 
make it continue to rise for some time after : much 
more must it do so when the attraction is only 
diminished, as a little impulse given to a moving 
ball will cause it still to move farther than other- 
wise it could have done, and as experience 
shows that the day is hotter about three in the 
afternoon than when the sun is on the meridian, 
because of the continual addition to the heat al- 
ready accumulated. 

The tides do not answer always to the same dis- 
tance of the moon from the meridian at the same 
places, but are variously affected by the action of 
the sun, which brings them on sooner when the 
moon is in her first and third quarters, and keeps 
them back later when she is in her second and 
fourth quarters, because in the former case the tide 
raised by the sun alone would be earlier than the 
tide raised by the moon, and in the latter case later. 
The moon goes round the earth in an elliptic 
orbit, and therefore she approaches nearer to the 
earth than her mean distance, and recedes farther 
from it, in every lunar month. When she is near- 
est she attracts strongest, and so raises the tides 
most: the contrary happens when she is farthest, 
because of her weaker attraction. When both 
luminaries are in the equator, and the moon at her 
least distance from the earth, she raises the tides 



highest of all, especially at her conjunction and 
opposition, both because the equatorial parts have 
the greatest centrifugal force from their describing 
the largest circle, and from the concurring actions 
of the sun and moon. At the change, the attrac- 
tive forces of the sun and moon being united, they 
diminish the gravity of the waters under the moon, 
and their gravity on the opposite side is diminished 
by means of a greater centrifugal force. At the 
full, whilst the moon raises the tide under and 
opposite to her, the sun, acting in the same line, 
raises the tide under and opposite to him ; whence 
their conjoint effect is the same as at the change, 
and in both cases occasion what we call the spring 
tides. But at the quarters, the sun's action on the 




waters at and H diminishes the effect of the 
moon's action on the waters at Z and N, so that 
they rise a little under and opposite to the sun at 
and H, and fall as much under and opposite to the 
moon at Z and N, making what we call the neap 
tides, because the sun and moon then act cross-wise 
to each other. But, strictly speaking, these tides 
happen not till some time after, because in this, as 
in other cases, the actions do not produce the 
greatest effect when they are at the strongest, but 
some time afterward. 

Another effect of the combination of the solar 
and lunar tides is what is called the priming and 
lagging of the tides. If the moon alone existed, and 
moved in the plane of the equator, the tide-day 
( i. e. the interval between two successive arrivals 
at the same place of the same vertex of the tide- 
wave) would be the lunar day formed by the com- 



WONDERS OF THE HEAVENS 



255 



bination of the moon's sidereal period and that of 
the earth's diurnal motion. Did the sun exist alone, 
and move always in the equator, the tide-day 
would be the mean solar day. The actual tide- 
day, then, or the interval of the occurrence of two 
successive maxima of their superposed waves, will 
vary as the separate waves approach to or recede 
from coincidence; because, when the vertices of 
two waves do not coincide, their joint height has 
its maximum at a point intermediate between them. 
This variation from uniformity in the lengths of 
successive tide-days is particularly to be remarked 
about the time of the new and full moon. 

The sea being thus put in motion, would continue 
to ebb and flow for several times, even though the 
sun and moon were annihilated, or their influence 
should cease; as if a basin of water were agitated, 
the water would continue to move for some time 
after the basin was left to stand still; or like a 
pendulum, which, having been put in motion by the 
hand, continues to make several vibrations without 
any new impulse. 

The declination of the sun and moon materially 
affect the tides. We shall illustrate this effect as 
regards the moon. When the moon is in the equa- 
tor, the tides are equally high in both parts of the 
lunar day, or time of the moon's revolving from the 
meridian to the meridian again, which is twenty-four 
hours and forty-eight minutes. But as the moon 
declines from the equator towards either pole, the 
tides are alternately higher and lower at places 
having north or south latitude. For the tide of the 
highest elevations, which is that under the moon, 
follows her towards the pole to which she is nearest, 
and the other declines towards the opposite pole, 
each elevation describing parallels as far distant 
from the equator, on opposite sides, as the moon 
declines from it to either side, and consequently the 
parallels described by these elevations of the water 
are twice as many degrees from one another as 
the moon is from the equator, increasing their dis- 
tance as the moon increases her declination till it 
be at the greatest, when the said parallels are, at 
a mean state, forty-seven degrees from one another, 
and on that day the tides are most unequal in 



their heights. As the moon returns toward the 
equator, the parallels described by the opposite 
elevations approach towards each other until the 
moon comes to the equator, and then they coincide. 
As the moon declines toward the opposite pole, 
at equal distances, each elevation describes the 
same parallel in the other part of the lunar day 
which its opposite elevation described before. 
Whilst the moon has north declination, the greatest 
tides in the northern hemisphere are when she is 
above the horizon, and the reverse whilst her 




declination is south. Let N E S Q, be the earth, 
N C S its axis, E Q, the equator, T r the tropic of 
cancer, tn the tropic of Capricorn, ab the arctic 
circle, cd the antarctic, N the north pole, S the 
south pole, M the moon, F and G the two emi- 
nences of water, whose lowest parts are at a and 
d Fig. 1, at N and S Fig. 2, and at h and c 
Fig. 3, always ninety degrees from the highest. 
Now, when the moon is in her greatest north decli- 
nation at M, the highest elevation G under her is 
on the tropic of cancer T r, and the opposite 
elevation F on the tropic of Capricorn t n, and 
these two elevations describe the tropics by the 
earth's diurnal rotation. All places in the northern 



256 



WONDERS OF THE HEAVENS. 



hemisphere E N Q, have the highest tides when 
they come into the position br Q, under the moon, 
and the lowest tides when the earth's dim-nal 
rotation carries them into the position a T E on 
the side opposite to the moon. The reverse happens 
at the same time in the southern hemisphere ESQ, 
as is evident to sight. The axis of the tides aC d 
has now its poles a and d (being always ninety 
degrees from the highest elevations) in the arctic 
and antarctic circles, and therefore it is plain that 
at these circles there is but one tide of flood, and 
one of ebb, in the lunar day; for when the point 
a revolves half round to b in twelve lunar hours 
it has a tide of flood, but when it comes to the 
same point a again in twelve hours more it has 
the lowest ebb. In seven days afterward, the 
moon M comes to the equinoctial circle, and is 
over the equator E Q, when both elevations de- 
scribe the equator, and, in both hemispheres, at 
equal distances from the equator, the tides are 
equally high in both parts of the lunar day. All 
the phenomena being reversed when the moon 
has south declination to what they were when her 
declination was north, they require no farther 
description. 

In the three last-mentioned figures, the earth is 
projected on the plane of the meridian; but, in 
order to describe a particular phenomenon, we 
project it on the plane of the ecliptic. Let H Z N 
be the earth and sea, (see figure on page 254,) 
FED the equator, T the tropic of cancer, C the 
arctic circle, P the north pole, and the curves 
1,2, 3, &c. twenty-four meridians or hour-circles 
intersecting each other in the poles. A G M is the 
moon's orbit, S the sun, M the moon, Z the water 
elevated under the moon, and N the opposite equal 
elevation. As the lowest parts of the water are 
always ninety degrees from the highest, when the 
moon is in either of the tropics (as at M) the eleva- 
tion Z is on the tropic of Capricorn, and the 
opposite elevation N on the tropic of cancer, the 
low-water circle H C touches the polar circles at 
C, and the high- water circle E T P 6 goes over the 
poles at P, and divides every parallel of latitude 
into two equal segments. In this case, the tides 



upon every parallel are alternately higher and 
lower, but they return at equal times. The point 
T, for example, on the tropic of cancer (where the 
depth of the tide is represented by the breadth of 
the dark shade) has a shallower tide of flood at T 
than when it revolves half round from thence to 6, 
according to the order of the numeral figures ; but it 
revolves as soon from 6 to T as it did from Tto6. 
When the moon is in the equinoctial, the elevations 
Z and N are transferred to the equator at and H, 
and the high and low-water circles have moved into 
each other's former places, in which case the tides 
return in unequal times, but are equally high in 
both parts of the lunar day; for a place at 1, 
(under D,) revolving as formerly, goes sooner from 
1 to 11 (under F) than from 11 to 1, because the 
parallel it describes is cut into unequal segments 
by the high-water circle H C ; but the points 1 
and 11 being equidistant from the pole of the tides 
at C, which is directly under the pole of the moon's 
orbit M G A, the elevations are equally high in 
both parts of the day. 

And thus it appears, that, as the tides are 
governed by the moon, they must turn on the axis 
of the moon's orbit, which is inclined twenty-three 
and a half degrees to the earth's axis at a mean 
state ; and therefore the poles of the tides must be 
so many degrees fi'om the poles of the earth, or in 
opposite points of the polar circles, going round 
these circles in every lunar day. It is true, that, 
according to Fig. 3, when the moon is vertical to 
the equator E C Q, the poles of the tides seem to 
fall in with the poles of the world N and S ; but 
when we consider that F H G is under the moon's 
orbit, it will appear, that, when the moon is over H, 
in the tropic of Capricorn, the north pole of the 
tides (which can be no more than ninety degrees 
from under the moon) must be at c in the arctic 
circle, not at N, the north pole of the earth, and, 
as the moon ascends from H to G in her orbit, the 
north pole of the tides must shift from c to a in the 
arctic circle, and the south pole as much in the 
antarctic. 

It is not to be doubted but that the earth's j 
quick rotation brings the poles of the tides nearer i 



WONDERS OF THE HEAVENS. 



257 



to the poles of the world than they would be if the 
earth were at rest and the moon revolved about it 
only once a month, for otherwise the tides would be 
more unequal in their heights and the times of their 
returns than we find they are. But how near the 
earth's rotation may bring the poles of its axis and 
those of the tides together, or how far the pre- 
ceding tides may affect those which follow so as to 
make them keep up nearly to the same heights 
and times of ebbing and flowing, is a problem more 
fit to be solved by observation than by theory. 

Those who have opportunity to make observa- 
tions, and choose to satisfy themselves whether the 
tides are really affected in the above manner by 
the different positions of the moon, especially as to 
the unequal times of their returns, may take this 
general rule for knowing when they ought to be so 
affected : — When the earth's axis inclines to the 
moon, the northern tides, if not retarded in their 
passage through shoals and channels or affected 
by the winds, ought to be greatest when the moon 
is above the horizon, least when she is below it, 
and quite the reverse when the earth's axis declines 
from her, but in both cases at equal intervals of 
time. When the earth's axis inclines sidewise to 
the moon, both tides ought to be equally high; but 
they happen at unequal intervals of time. In every 
lunation, the earth's axis inclines once to the moon, 
once from her, and twice sidewise to her, as it 
does to the sun every year, because the moon 
goes round the ecliptic every month, and the sun 
but once in a year. In summer, the earth's axis 
inclines towards the moon when new, and therefore 
the day-tides in the north ought to be highest, and 
night-tides lowest, about the change ; at the full the 
reverse. At the quarters, they ought to be equally 
high, but unequal in their returns, because the 
earth's axis then inclines sidewise to the moon. In 
winter, the phenomena are the same at full moon 
as in summer at new. In autumn, the earth's axis 
inclines sidewise to the moon when new and full ; 
therefore the tides ought to be equally high, and 
unequal in their returns, at these times. At the 
first quarter, the tide of flood should be least when 

the moon is above the horizon, greatest when she 
33 



is below it ; and the reverse at her third quarter. 
In spring, the phenomena of the first quarter 
answer to those of the third quarter in autumn; 
and vice versa. The nearer any time is to either of 
these seasons, the more the tides partake of the 
phenomena of these seasons ; and in the middle 
between any two of them, the tides are at a mean 
state between those of both. 

The deviation of the time of high and low water 
at any port or harbor from the culmination of the 
luminaries, is called the "establishment" of that 
port. If the water were without inertia, and fi-ee 
from obstruction, either owing to the friction of the 
bed of the sea, the narrowness of channels along 
which the wave has to travel before reaching the 
port, their length, &c., &lc., the times above dis- 
tinguished would be identical. But all these causes 
tend to create a difference, and to make that dif- 
ference not alike at all ports. The observation of 
the establishment of harbors, is a point of great 
maritime importance ; nor is it of less consequence, 
theoretically speaking, to a knowledge of the true 
distribution of the tide-waves over the globe. In 
making such observations, care must be taken not 
to confound the time of slack water when the 
current caused by the tide ceases to flow visibly 
one way or the other, and that of high or low 
water, when the level of the surface ceases to rise 
or fall. 

These are the principal phenomena of the tides ; 
and, where no local circumstances interfere, the 
theory and facts will be found to agree nearly. It 
must be observed that what has been said generally 
relates only to such places as lie open to the ocean ; 
for of all the causes of difference in the height of 
tides, local situation is the most influential. The 
variations from this cause are almost beyond belief 
Thus the Mediterranean and Baltic seas have very 
small elevations, because the inlets by which they 
communicate with the ocean are so narrow that 
they cannot in a short time receive or discharge 
enough to raise or sink their surfaces much. 
While at Bristol, England, the tide sometimes rises 
thirty feet, and at Cumberland, in the Bay of Fundy, 
it is said to rise seventy feet. 



258 



WONDERS OF THE HEAVENS 



There are, also, from the same cause, great varia- 
tions in the time of the tides. 

The tides are so retarded in their passage 
through different shoals and channels, and other- 
wise so variously affected by striking against capes 
and headlands, that to different places they happen 
at all distances of the moon from the meridian, con- 
sequently at all hours of the lunar day. 

The time of full sea at Boston differs from that 
at New Bedford three hours and a half, and from 
that at Albany four hours and twelve minutes; and 
between the two last-mentioned places it differs 
seven hours and forty-two minutes, taking place 
three and a half hours earlier at New Bedford, and 
four and one fifth hours later at Albany, than at 
Boston. 

What has been said of the ocean may likewise 
be applied to the air, for, the surface of the atmo- 
sphere being nearer to the moon than the surface 
of the sea, it is plain that the aerial tides must be 
more considerable than those of the ocean; and, on 
this account, it should seem to follow that the 
mercury in the barometer would sink lower than at 
other times when the moon passes the meridian, 
because the action on the particles of air must at 
that time make them lighter. Delicate observations 
have been able to render these aerial tides sensible 
and measurable. The effect, however, is extremely 
minute, which would be expected when it is con- 
sidered, that, in proportion as these particles are 
rendered lighter, a greater number of them will be 
accumulated, and thus the pressure will be nearly 
the same as before, and the mercury will be 
scarcely affected at all. 

We make the following extract from an article in 
one of the numbers of Silliman's Journal of Science 
relative to tides, by W. C. Redfield, who, after 
recapitulating some of the evidence showing the 
absence of the usual tides at the Society Islands, 
and in some other parts of the Pacific Ocean, con- 
tinues as follows : — 

"It must therefore be admitted that there is a 
suspension or neutralization of the lunar tide-wave 
in the region in which those islands are situated. 
We find, too, that in the Atlantic it is high water 



on the coast of Surinam about five o'clock on the 
days of the new and full of the moon, and the flood 
runs to the westward; at the windward islands 
of the West Indies, the tide is some one or two 
hours later, and, though exposed to the whole tide 
range of the Atlantic, the tides are very weak and 
irregular, not rising more than at the Society 
Islands ; on the southern coast of the United 
States, and at the Island of Bermuda in the At- 
lantic, it is high water about seven o'clock, and 
the flood tide in the offing at the latter place 
running to the northeast; on the southern coast of 
Rhode Island and Massachusetts, it is high water 
from seven to eight o clock ; on the south-eastern 
coast of Nova Scotia and Newfoundland, it is high 
water from eight to nine o'clock, the flood tide oflf 
the latter coast also running north-eastwardly ; at 
the Azores, or Western Islands, in latitude thirty- 
eight degrees north, near the middle of the Atlantic, 
it is high water about twelve o'clock, and the flood 
runs to the eastward; finally, it is high water on 
the western coasts of Ireland and Spain about two 
o'clock — all on the same days. These statements 
are approximated from the American Coast Pilot 
and other • authorities, care being taken to avoid 
the retarding effects of local obstructions as far as 
possible, by timing them from the most extraneous 
positions of coast towards the open ocean." 

"Viewing these phenomena in connection with 
some other facts, I was led to suspect that the 
great tide-wave performs an actual circuit in each 
of the great oceanic basins on both sides of the 
equator, passing westwardly in the equatorial 
latitudes, and returning eastwardly in the higher 
latitudes, above twenty-five degrees or thirty 
degrees north and south, and analogous to the 
course which is pursued, as can be demonstrably 
shown, by the great currents both of the ocean and 
the atmosphere. If such be the operation of the 
tides, certain regions in mid-ocean would form the 
foci, or neutral points, in these great elliptical cir- 
cuits, and would be but slightly, if at all, affected 
by the ordinary tides. The elaborate investigation 
of cotidal lines in which professor Whewell is 
engaged, will probably show whether the course 



WONDERS OF THE HEAVENS 



259 



of the great tide-wave be from the Southern Ocean, 
northwardly, through the entire length of the 
Atlantic, and in disregard of the direct lunar influ- 
ence in this ocean, as would seem to be indicated 
in his late paper on that subject. The greatest 
difficulty attending the inquiry, is in procuring 
correct observations from those islands and exter- 
nal points of coast which bear most decidedly 
upon the question." 



SECTION IV. 

Solar and sidereal days — Equation of time — Inequality arising from 
the obliquity of the ecliptic — That caused by the unequal motion 
of the earth in its orbit — Deductions respecting the equation 
throughout the year — Mean and apparent time agree but four 
days in the year — Calendar — Standards of time — Their inconven- 
ience — Gregorian method of correcting the calendar — Grecian 
calendar — Roman calendar — Its correction by Julius Csesar — Per- 
sian calendar— Subdivisions of the year — Cycle — Dionysian period 
— Dominical letters — Julian period. 

The fixed stars appear to go round the earth in 
twenty-three hours, fifty-six minutes, and four 
seconds, and the sun in twenty-four hours, so that 
the stars gain three minutes and fifty-six seconds 
upon the sun every day, which amounts to one 
diurnal revolution in a year ; and, therefore, in 
three hundred and sixty-five days as measured by 
the returns of the sun to the meridian, there are 




three hundred and sixty-six days as measured by 
the stars returning to it. The former are called 
solar days, and the latter sidereal. 

The diameter of the earth's orbit is but a physi- 
cal point in proportion to the distance of the stars. 
For this reason, and the earth's uniform motion 
on its axis, a given meridian will revolve from 
any star to the same star again in each absolute 
revolution of the earth on its axis, without the 
least perceptible difference of time shown by a 
clock that goes exactly true. 

If the earth had a diurnal, without an annual, 
motion, any given meridian would revolve from the 
sun to the sun again in the same space of time as 
from any star to the same star again, because the 
sun would never change his place with respect to 
the stars. But, as the earth advances almost a 
degree eastward in its orbit during the time that it 
is turning eastward round its axis, whatever star 
passes over the meridian on any day with the sun 
will pass over the same meridian on the next day 
when the sun is nearly a degree from it, or sooner 
than the sun by three minutes and fifty-six seconds. 
If the year contained only three hundred and sixty 
days, as the ecliptic does three hundred and sixty 
degrees, the sun's apparent place, so far as his 
motion is equable, would change a degree every 
day, and then the sidereal day would be just 
four minutes shorter than the solar. 



Let ABCDEFGHIKLM be the orbit in 
which the earth goes round the sun every year 
according to the order of the letters, that is, from 



west to east, turning round its axis the same way 
from the sun to the sun again every twenty-four 
hours. Let S be the sun, and R a fixed star at 



260 



WONDERS OF THE HEAVENS 



such an immense distance that the diameter of the 
earth's orbit bears no sensible proportion to that 
distance. Let Nm be any particular meridian of 
the earth, and N a given point or place upon that 
meridian. When the earth is at A, the sun S hides 
the star R, which would always be hidden if the 
earth did not remove from A, and consequently, 
as the earth turns round its axis, the point N would 
always come round to the sun and star at the same 
time. But when the earth has advanced, suppose 
a twelfth part of its orbit from A to B, its motion 
round its axis will bring the point N a twelfth part 
of a natural day, or two hours, sooner to the star 
than to the sun, (for the angle N B w is equal to the 
angle A S B,) and therefore any star which comes 
to the meridian at noon with the sun when the 
earth is at A, will come to the meridian at ten in 
the forenoon when the earth is at B. When the 
earth comes to C, the point N will have the star 
on its meridian at eight in the morning, or four 
hours sooner than it comes round to the sun, for it 
must revolve from N to w before it has the sun in 
its meridian. When the earth comes to D, the 
point N will have the star on its meridian at six in 
the morning ; but that point must revolve six hours 
more from N to n before it has mid-day by the sun, 
for now the angle A S D is a right angle, and so is 
N D n — that is, the earth has advanced ninety de- 
grees in its orbit, and must turn ninety degrees on 
its axis to carry the point N from the star to the 
sun, for the star always comes to the meridian 
when Not is parallel to RS A, because DS is but 
a point in respect of R S. When the earth is at E, 
the star comes to the meridian at four in the morn- 
ing; at F, at two in the morning; and at G, the 
earth having gone half round its orbit, N points to 
the star R at midnight, it being then directly oppo- 
site to the sun, and therefore, by the earth's diur- 
nal motion, the star comes to the meridian twelve 
hours before the sun. When the earth is at H, the 
star comes to the meridian at ten in the evening; 
at I, it comes to the meridian at eight, that is, six- 
teen hours before the sun ; at K, eighteen hours 
before him ; at L, twenty hours ; at M, twenty-two ; 
and at A, at the same time with the sun again. 



Thus it is plain that an absolute revolution of the 
earth on its axis (which is always completed when 
any particular meridian comes to be parallel to its 
situation at any time of the day before) never brings 
the same meridian round from the sun to the sun 
again ; for the earth requires as much more than 
one turn on its axis to finish a natural day, as it has 
gone forward in that time, which, at a mean state, 
is a 365th part of a circle. Hence, in three hun- 
dred and sixty-five days the earth revolves three 
hundred and sixty-six times round its axis ; and, as 
a revolution of the earth on its axis completes a 
sidereal day, the number of sidereal days in a year 
must be one more than that of the solar days, be 
this last number what it may. This is true in re- 
spect to all the other planets as well as the earth, 
one revolution being lost with respect to the num- 
ber of solar days in a year by the planet's going 
round the sun, just as it would be lost to a traveller 
who was going round the earth. He would lose one 
day by following the apparent diurnal motion of the 
sun, and consequently would reckon one day less 
at his return (let him take what time he would to 
go round the earth) than those who remained all the 
while at the place from which he set out. So, if 
there were two earths revolving equably on their 
axes, and if one remained at A until the other 
travelled round the sun from A to A again, that 
earth which kept its place at A would have its solar 
and sidereal days always of the same length, and 
would have had one solar day more than the other at 
its return. Hence, if the earth turned but once 
round its axis in a year, and if that turn was made 
the same way as the earth goes round the sun, 
there would be continual day on one side of the 
earth, and continual night on the other. 

Tables divided into two parts have been con- 
stucted, showing first how much of the celestial 
equator passes over the meridian in any given part 
of a mean solar day, and secondly the accelera- 
tions of the fixed stars. The latter part affords us 
an easy method of knowing whether our clocks and 
watches go true; for if, through a small hole in a 
window-shutter, or in a thin plate of metal fixed 
to a window, we observe at what time any star 



WONDERS OF THE HEAVENS 



261 



disappears behind a chimney, or corner of a house, 
at a little distance, and if the same star disappears 
the next night three minutes fifty-six seconds sooner 
by the clock or watch, and on the second night 
seven minutes fifty-two seconds sooner, the third 
night eleven minutes forty-eight seconds sooner, 
and so on, it is an infallible sign that the time-piece 
goes true, otherwise it does not go true, and must 
be regulated accordingly; and, as the disappearing 
of a star is instantaneous, we may depend on this 
information to half a second. 

A great number of the most important elements 
involved in astronomical researches are variable in 
their amount. Their variations, however, general- 
ly succeed each other in a certain order, and are 
confined within certain limits; and when these 
limits and all the varying values are ascertained, 
it is of course possible to take an average among 
them, and this average value is termed a mean 
value. 

It is, indeed, always possible to take an average 
between any number of observations, or of ascer- 
tained values of a particular element ; but, unless 
the observations are so taken that the whole course 
of the variation is included, it is not usual to call 
the average a mean value, or rather it is not the 
absolute mean value of the thing itself — it is only its 
average or mean value for a certain time. For 
instance, we have already seen that the length of 
the day, considered as the interval from sunrise to 
sunset, is continually varying, but that it goes 
through all its changes in the interval from one 
solstice to another. Its average duration for this 
whole time, then, is its mean value. It is a little 
more than twelve hours, and it is very nearly the 
same everywhere. It would be everywhere exactly 
twelve hours, if the sun always moved at the same 
rate, and there were no parallax or refraction. An 
average, however, might be taken of the lengths 
of this day for a portion only of this interval : for 
instance, from the vernal equinox to the summer 
solstice : the length of the shortest day would be a 
little more than twelve hours, and the average 
length, at Belle Isle, for example, about fourteen 
hours and three quarters. This would be a correct 



average of the lengths observed ; but, as the time 
of observation would not comprehend all the varia- 
tions of the element in question, it would not be 
the mean length of the day absolutely, though it 
might be called the mean length for the period of 
observation. 

In the same manner as we have taken an instance 
of mean duration, we might have an instance of 
mean motion, that is to say, if a body moves with 
a variable motion ; but if the whole course of its 
variation is ascertained, its average rate of motion 
during this whole course may be found, and this 
will be called its mean motion. A body moving with 
this mean motion, and of course moving uniformly 
during the whole time occupied by the whole series 
of the real motions, would move through the same 
space as the real body ; but its place at many or all 
of the intermediate periods would be different from 
the place of the real body, on account of the differ- 
ence between the real and mean motions. The 
place of a body so moving, or the place which the 
real body would occupy on the supposition that it 
moved uniformly, and described in the time occu- 
pied by the whole series of its real motions the 
same spaces which it actually does, is called the 
mean place of the body. In the same manner, any 
event that happens at various intervals which 
succeed each other in a certain and recurring 
order will have a mean time of occurrence. 

Now it very generally happens in astronomy that 
it is less inconvenient first to compute the mean 
place of a body, or the mean time of an event, and 
then to ascertain the difference between the mean 
and the true, than to go through the computations 
necessary to find the true time and place in the 
first instance. 

When once the mean values have been ascer- 
tained, the mean motion of a body during a known 
period, its mean place at a known time, the mean 
time of the occurrence of a given event are easily 
found ; for the intervals of the mean time and the 
rate of the mean motion being always the same, 
we only want to know how often the event has 
occurred, or how long the motion has been con- 
tinued. If, from a consideration of the manner in 



262 



WONDERS OF THE HEAVENS. 



which the difference between the true and mean 
values arises, we can ascertain the amount of that 
difference in each particular instance, we can find 
what is to be added to, or subtracted from, the 
mean value to arrive at the true, and the quantity 
so added or substracted is called an equation. The 
mean value thus leads to the true value, and of 
course it furnishes an approximation to it ; and as 
the subjects of astronomical inquiry generally have 
their variations confined within narrow limits so 
that the difference between the true and mean 
motions, times, and places is not very great, the 
approximation is not very distant. 

We shall find several instances of the application 
of the terms above explained, and of the use made 
of these mean values and results, in treating of the 
equation of time, of which we are about to speak, 
and then the more obvious appearances of the sun, 
and their principal effects, will have been suf- 
ficiently explained. 

The earth's motion on its axis being perfectly 
uniform, and equal at all times of the year, the 
sidereal days are always of the same length; and 
so would the solar or natural days be if the earth's 
orbit were a perfect circle, and its axis perpendi- 
cular to its orbit. But the earth's diurnal motion 
on an inclined axis, and its annual motion in an 
elliptic orbit, cause the sun's apparent motion in 
the heavens to be unequal, for sometimes he re- 
volves from the meridian to the meridian again in 
somewhat less than twenty-four hours, as shown by 
a well-regulated clock, and at other times in some- 
what more. 

Tables of the equation of natural days are given 
in some astronomies, showing the time that ought 
to be pointed out by a well-regulated clock or 
watch, every day of the year, at the precise mo- 
ment of solar noon, that is, when the sun's centre 
is on the meridian, or when a sun-dial shows it to 
be precisely twelve. By these we should find, for 
example, that, on the 5th of January, in leap-year, 
when the sun is on the meridian, it ought to be five 
minutes and fifty-one seconds past twelve by the 
clock, and on the 15th of May, when the sun is 
on the meridian, the time by the clock should be 



fifty-five minutes and fifty-seven seconds past 
eleven. In the former case, the clock is five 
minutes and fifty-one seconds faster than the sun ; 
and in the latter case, the sun is four minutes and 
three seconds faster than the clock. 

In order to set a sun-dial, it will be necessary to 
fix accurately the position of the meridian, and the 
easiest and most expeditious way of doing this is as 
follows : Make four or five concentric circles, about 
a quarter of an inch from one another, on a fiat 
board about a foot in breadth, and let the outer 
circle be but little less than the board will contain. 
Fix a pin perpendicularly in the centre, and of such 
a length that its whole shadow may fall Avithin the 
innermost circle for at least four hours in the 
middle of the day. The pin ought to be about an 
eighth part of an inch thick, and to have a round, 
blunt point. The board being set exactly level in 
a place where the sun shines, suppose from eight 
in the morning till four in the afternoon, (for about 
these hours the end of the shadow should fall 
within all the circles,) watch the times in the fore- 
noon when the extremity of the shortening shadow 
just touches the several circles, and there make 
marks: then, in the afternoon of the same day, 
watch the lengthening shadow, and where its end 
touches the several circles in going over them 
make marks also : lastly, with a pair of compasses, 
find exactly the middle point between the two 
marks on any circle, and draw a straight line from 
the centre to that point. This line will be covered 
at noon by the shadow of a small upright wire, 
which should be put in the place of the pin. The 
reason for drawing several circles is, that, in case 
one part of the day should prove clear and the 
other part somewhat cloudy, if you miss the time 
when the point of the shadow should touch one 
circle, you may perhaps catch it in touching 
another. The best time for drawing a meridian 
line in this manner is about the summer solstice, 
because the sun changes his declination with the 
least, and his altitude with the greatest, rapidity at 
that time. 

If the casement of a window on which the sun 
shines at noon be exactly upright, you may draw a 



EMnBSrt5P5Wf» 



WONDERS OF THE HEAVENS 



263 



line along the edge of its shadow on the floor when 
the shadow of the pin is exactly on the meridian 
line of the board ; and, as the motion of the shadow 
of the casement will be much more sensible on the 
floor than that of the shadow of the pin on the 
board, you may know to a few seconds when it 
touches the meridian line on the floor, and so regu- 
late your clock for the day of observation by that 
line and the equation tables before mentioned. 

As the equation of time, or difference between 
the time shown by a well-regulated clock and a 
sun-dial, depends upon two causes, namely, the 
obliquity of the ecliptic, and the unequal motion 
of the earth in it, we shall explain first the effects 
of these causes separately considered, and then the 
united effects resulting from their combination. 

The earth's motion on its axis being perfectly 
equable, or always at the same rate, and the plane 
of the equator being perpendicular to its axis, it is 
evident that in equal times equal portions of the 
equator will pass over the meridian, and so would 
equal portions of the ecliptic if it were parallel to, 
or coincident with, the equator. But, as the eclip- 
tic is oblique to the equator, the equable motion 
of the earth on its axis carries unequal portions 
of the ecliptic over the meridian in equal times, 
the difference being proportional to the obliquity ; 
and, as some parts of the ecliptic are much more 
obliquely situated with respect to the equator than 
others, those differences are unequal among them- 
selves. Therefore, if two sum should start either 
from the beginning of Aries or Libra, and continue 
to move through equal arcs in equal times, one in 
the equator, and the other in the ecliptic, the 
equatorial sun would always return to the meridian 
in twenty-four hours of time measured by a well- 
regulated clock, but the sun in the ecliptic would 
return to the meridian sometimes sooner, and 
sometimes later, than the equatorial sun, and only 
at the same moments with him on four days of the 
year, namely, the 21st of March, when the sun 
enters Aries, the 21st of June, when he enters 
Cancer, the 23d of September, when he enters 
Libra, and the 21st of December, when he enters 
Capricorn. At these times, therefore, the differ- 



ence between mean and apparent time caused by 
the obliquity of the ecliptic would be least, and 
about the 5th of February, the 6th of May, the 
8th of August, and the 8th of November this dif- 
ference would be greatest. As there is only one 
sun, and his apparent motion is always in the 
ecliptic, let us call him the real sun, and the other, 
which is supposed to move in the equator, the 
fictitious sun. To this last, the motion of a well- 
regulated clock always answers. 

Let Z T 2r :2: be the earth, Z F R 2r its axis, 
abed e^ &c. the equator, ABODE, &c. the 




northern half of the ecliptic from °f to =c= on the 
side of the globe next the eye, and M N P, &c. 
the southern half on the opposite side from =^ to T. 
Let the points at A, B, C, D, E, F, &c. quite 
round from T to T again bound equal portions of 
the ecliptic gone through in equal times by the 
real sun, and those at a, b, c, d, e,f, &c. equal 
portions of the equator described in equal times by 
the fictitious sun, and let Z T ^r be the meridian. 

As the real sun moves obliquely in the ecliptic, 
and the fictitious sun directly in the equator, with 
respect to the meridian, a degree, or any number 
of degrees, between "f and F on the ecliptic must 
be nearer the meridian Z T ^, than a degree, or 
any corresponding number of degrees on the equator 
from °f to/, and the more so as they are the more 
oblique; and therefore the true sun comes sooner 



264 



WONDERS OF THE HEAVENS. 



to the meridian every day whilst he is in the 
quadrant of F than the fictitious sun does in the 
quadrant <f f. For this reason, the solar noon pre- 
cedes noon by the clock until the real sun comes 
to F and the fictitious sun to /, which two points, 
being equidistant fi:"om the meridian, both suns will 
come to it precisely at noon by the clock. 

Whilst the real sun describes the second quadrant 
of the ecliptic F G H I K L fi'om s to £i: , he comes 
later to the meridian every day than the fictitious 
sun moving through the second quadrant of the 
equator from f to j^, for the points at G, H, I, K, 
and L being farther from the meridian than their 
corresponding points at g, h, i, k, and I, they must 
be later in coming to it, and as both suns come at 
the same moment to the point :ii, they come to the 
meridian at the moment of noon by the clock. 

In departing from Libra through the third 
quadrants, the real sun going through M N P Q, 
towards i^ at R, and the fictitious sun through 
m n b p q towards r, the former comes to the 
meridian every day sooner than the latter until 
the real sun comes to vj and the fictitious sun to r, 
and then they both come to the meridian at the 
same time. 

Lastly, as the real sun moves equably through 
STUVW, from \S towards T, and the fictitious 
sun through s tuv w, from r towards T, the former 
comes later every day to the meridian than the 
latter until they both arrive at the point f, and 
then it is noon at the same time both by the clock 
and the sun. 

This part of the equation of time may perhaps be 
somewhat difficult to understand by a figure, because 
both halves of the ecliptic seem to be on the same 
side of the globe, but it may be made very easy to 
any person who has a real globe before him. By 
putting small patches on every tenth or fifteenth 
degree both of the equator and ecliptic, beginning 
at Aries, he will, on turning the globe slowly 
round westward, see all the patches from Aries to 
Cancer come to the brazen meridian sooner than 
the corresponding patches on the equator ; all those 
from Cancer to Libra will come later to the 
meridian than their corresponding patches on the 



equator; those from Libra to Capricorn sooner, 
and those from Capricorn to Aries later ; and the 
patches at the beginnings of Aries, Cancer, Libra, 
and Capricorn, being either on, or even with those 
on the equator, show that the two suns either meet 
there, or are even with one another, and so come 
to the meridian at the same moment. 

Let us suppose that there are two balls moving 
equably round a celestial globe by clock-work, (one 
always keeping in the ecliptic, and gilt with gold 
to represent the real sun, and the other keeping in 
the equator, and silvered to represent the fictitious 
sun,) and that whilst these balls move once round 
the globe according to the order of signs, the clock 
turns the globe three hundred and sixty-six times 
round its axis westward. The stars will make 
three hundred and sixty-six diurnal revolutions 
from the brazen meridian to the same again, and 
the two balls representing the real and fictitious 
suns, always going farther eastward from any given 
star, will come later than that star to the meridian 
every following day, and each ball will make three 
hundred and sixty-five returns to the meridian, 
coming equally to it at the beginnings of Aries, 
Cancer, Libra, and Capricorn : but in every other 
point of the ecliptic the gilt ball will come either 
sooner or later to the meridian than the silvered 
ball, like the patches above mentioned. This would 
be a good way of showing the reason why any 
given star, which, on a certain day of the year 
comes to the meridian with the sun, passes over 
that meridian sooner every following day, so that 
in a twelvemonth it comes to the meridian with the 
sun again; as also of showing the reason why the 
real sun comes to the meridian sometimes sooner, 
sometimes later, than noon as shown by the clock, 
and, on four days of the year, at the same time, 
whilst the fictitious sun always comes to the meri- 
dian when it is twelve at noon by the clock. 

If the ecliptic were more oblique to the equator, 
the equal divisions from T to a: would come still 
sooner to the meridian Z o T than those marked 
A, B, C, D, and E do; for two divisions containing 
thirty degrees, from °f to the second dot, a little 
short of the figure 1, come sooner to the meridian 



WONDERS OF THE HEAVENS. 



265 



than one division containing only fifteen degrees, 
from °f to A, does, as the ecliptic now stands, and 
those of the second quadrant from a: to lO: would be 
as much later. The third quadrant would be as 
the first, and the fourth as the second. Also, 
where the ecliptic was most oblique, namely, about 
Aries and Libra, the difference would be greatest, 
and least about Cancer and Capricorn, where the 
obliquity was the least. 

We proceed to explain the second cause of the 
difference between mean and apparent time, name- 
ly, the inequality of the sun's apparent motion, 
which is slowest in summer when the sun is farthest 
from the earth, and most rapid in winter when he 
is nearest the earth. But the earth's motion on its 
axis is equable all the year round, and is performed 
from west to east, the same way that the sun ap- 
pears to change his place in the ecliptic. 

If the sun's motion were equable in the ecliptic, 
the whole difference between the equal time as 
shown by a clock, and the unequal time as shown 
by the sun, would arise from the obliquity of the 
ecliptic. But the sun's motion sometimes exceeds 
a degree in twenty-four hours, though generally 
it is less ; and when his motion is slowest any par- 
ticular meridian will return sooner to him than 
when his motion is most rapid, overtaking him in 
less time when he advances a less space than 
when he moves through a greater. 

If there were two suns moving in the plane of 
the ecliptic so as to go round it in a year, one 
describing an equal arc every twenty-four hours, 
and the other describing sometimes a less and 
sometimes a larger arc in twenty-four hours, and 
gaining at one time of the year what it lost at the 
opposite, it is evident that either of these suns 
would come sooner or later to the meridian than 
the other as it happened to be behind or before 
the other, and when they were both in conjunction 
they would come to the meridian at the same 
moment. 

As the real sun moves unequably in the ecliptic, 

let us suppose a fictitious sun to move equably in a 

circle coincident with the plane of the ecliptic. 

Let A B C D be the ecliptic or orbit in which the 

34 



real sun moves, and the dotted circle abed the 
imaginary orbit of the fictitious sun, each going 




round in a year according to the order of letters, 
or from west to east. Let H I K L be the earth 
turning round its axis the same wscy every twenty- 
four hours ; and suppose both suns to start from A. 
and a in a right line with the plane of the meridian 
E H at the same moment, the real sun at A being 
then at his greatest distance from the earth, at 
which time his motion is slowest, and the fictitious 
sun at a, whose motion is always equable because 
his distance from the earth is supposed to be always 
the same. In the same time that the meridian 
revolves from H to H again according to the order 
of the letters H I K L, the real sun moves from A 
to F, and the fictitious with a quicker motion from 
a to/ through a larger arc: therefore the meridian 
E H will revolve sooner from H to h under the real 
sun at F, than from H to ^ under the fictitious sun 
at /, and consequently it will then be noon by the 
sun-dial sooner than by the clock. 

As the real sun moves from A towards C, the 
rapidity of his motion increases all the way to C. 
Yet the fictitious sun gains so much upon the real 
sun soon after his departure from A, that the in- 
creasing velocity of the real sun does not bring him 
up with the fictitious sun till the former comes to 
C, and the latter to c, when each has gone half 
round its respective orbit; and then, both suns 



^^wfjj«-jyjijjA''ivKjMm 



266 



WONDERS OF THE HEAVENS, 



being in conjunction, the meridian E H, revolving 
to E K, comes to them at the same time, and there- 
fore it is noon by them both at the same moment. 

But the increased velocity of the real sun, being 
now at its maximum, carries him before the ficti- 
tious sun, and therefore the same meridian w^ill 
come to the latter sooner than to the former ; for 
while the fictitious sun moves from c to g, the real 
sun moves through a greater arc from C to G, 
consequently the point K has its noon by the clock 
when it comes to k, but not its noon by the sun till 
it comes to /. And although the velocity of the 
real sun diminishes all the way from C to A, and 
the fictitious sun by an equable motion is still 
coming nearer to the real sun, yet they are not in 
conjunction till the one comes to A, and the other 
to a, and then it is noon by them both at the same 
moment. 

Thus it appears that the solar noon is always 
later than noon by the clock whilst the sun goes 
from C to A, sooner whilst he goes from A to C, 
and at these two points, the sun and clock being 
equal, it is noon by them both at the same moment. 

The point A is called the sun's apogee, because 
when there he is at his greatest distance from the 
earth ; the point C his perigee, because when there 
he is at his least distance from the earth; and a 
right line, as A EC, drawn, through the earth's 
centre, from one of these points to the other, is 
called the line of the apsides. 

The distance that the sun has departed at any 
time from his apogee (not the distance he has to go 
to arrive at it, though ever so little) is called his 
anomaly, and is reckoned in signs and degrees, 
allowing thirty degrees to a sign. Thus, when the 
sun has gone suppose one hundred and seventy-four 
degrees from his apogee at A, he is said to be five 
signs and twenty-four degrees from it, which is his 
anomaly ; and when he has departed three hundred 
and fifty-five degrees from his apogee, he is said to 
be eleven signs and twenty-five degrees from it, 
although he is but five degrees short of A in coming 
round to it again. The distance that the sun 
would be at any time from apogee provided he 
moved uniformly in a circle is called his mean 



anomaly, and the period between his leaving and 
returning to a given situation with respect to the 
apogee is therefore called the anomalistic year. 

From what has been said above, it will be per- 
ceived that when the sun's anomaly is less than 
six signs, that is, when he is any where between 
A and C, in the half of his orbit ABC, the solar 
noon precedes the clock noon ; but when his ano- 
maly is more than six signs, that is, when he is 
any where between C and A, in the half of his orbit 
C D A, the clock noon precedes the solar. When 
his anomaly is nothing, that is, when he is in apo- 
gee at A, or when his anomaly is six signs exactly, 
that is, when he is in perigee at C, he comes to 
the meridian at the same moment with the fictitious 
sun, and then it is noon by them both at the same 
instant. 

Tables have been constructed showing that part 
of the equation of time which depends on the 
earth's unequal motion in its orbit. These, to- 
gether with the before-mentioned tables containing 
that part of the equation which results from the 
obliquity of the ecliptic, will enable us to calculate 
the absolute equation of time. If both of these equa- 
tions show the sun to be faster or slower than the 
clock, their sum is the absolute equation of time ; 
but if by one the sun is faster, and by the other 
slower, their difference is the absolute equation. 
Thus, suppose the equation depending on the sun's 
place be six minutes and forty-one seconds slow, 
and the equation depending on the sun's anomaly 
be four minutes and twenty seconds slow, their 
sum is the absolute equation, viz. eleven minutes 
and one second slow. But if one had been six 
minutes and forty-one seconds fast, and the other 
four minutes and twenty seconds slow, their diffe- 
rence would have been the equation, viz. two 
minutes and twenty-one seconds fast, because the 
greater quantity is too fast. 

We may now collect our results thus: In the 
course of the year there are four days, and only 
four, (namely, December 24th, April 15th, June 
15th, and September 1st,) when the apparent and 
mean time are the same, or the equation of time is 
nothing; and in the interval between the first and 



WONDERS OF THE HEAVENS. 



267 



second of these, and again in that between the 
third and fourth, the apparent is always later than 
the mean time, or the clock before the sun ; and 
between the second and third, and again between 
the fourth and first, the apparent is always earlier 
than the mean time, or the clock after the sun. 
These results correspond with those in the common 
tables of the equation of time. 

It is evident, also, from the manner in which these 
results have been deduced, that they depend en- 
tirely on the relative positions of the apogee and 
of the equinoxes. If these are fixed points, or hold 
always the same relative position, the results we 
have obtained will serve alike for every year. If 
they vary, the equation of time will vary also, and 
this consideration leads us to inquire whether there 
be any motion of the equinoxes, and whether the 
apogee and perigee be or be not fixed points. As 
far, also, as the magnitude of the equation is con- 
cerned, it is evident that any variation in the incli- 
nation of the ecliptic to the equator would affect it ; 
for the angle formed by lines drawn from Aries to 
the true and mean suns, and the declination of the 
sun at any point of the ecliptic, would both be 
affected by this change, and both these quantities 
are involved in the solution of that part of the 
question which arises from the motion of the sun 
in a plane inclined to the equator. 

In point of fact, it is found that the inclination 
of the ecliptic and equator does undergo some 
slight variation. This is not sufficient to produce 
any material alteration in the results, or to call for 
more extended notice here; but it furnishes one 
reason why the results obtained for the equation 
of time cannot, as far as their numerical values are 
concerned, apply accurately except to the particu- 
lar periods for which they are computed. 

Time, like distance, may be measured by com- 
parison with standards of any length, and all that 
is requisite for ascertaining correctly the length of 
any interval is to be able to apply the standard to 
the interval throughout its whole extent, without 
overlapping on the one hand, or leaving unmeasured 
vacancies on the other; to determine, without the 
possible error of a unit, the number of integer 



standards which the interval admits of being 
interposed between its beginning and end ; and to 
estimate precisely the fraction over and above an 
integer which remains when all the possible in- 
tegers are subtracted. 

But though all standard units of time are equally 
possible, theoretically speaking, all are not, practi- 
cally, equally convenient. The tropical year and 
the solar day are natural units, which the wants of 
man and the business of society force upon us, and 
compel us to adopt as our greater and lesser stand- 
ards in the measurement of time for all the 
purposes of civil life, and that, in spite of incon- 
veniences, which, did any choice exist, would speed- 
ily lead to the abandonment of one or the other. 
The principal of these are their incommensurability, 
and the want of perfect uniformity in one, at least, 
of them. 

The mean lengths of the sidereal day and year, 
when estimated on an average sufficiently large to 
compensate the fluctuations arising from nutation in 
the one and from inequalities of configuration in 
the other, are the two most invariable quantities 
which nature presents us with — the former by 
reason of the uniform diurnal rotation of the earth, 
the latter on account of the invariability of the axes 
of the planetary orbits. Hence it follows that the 
mean solar day is also invariable. It is otherwise 
with the tropical year. The motion of the equinoc- 
tial points varies not only from the retrogradation 
of the equator on the ecliptic, but also partly from 
that of the ecliptic on the orbits of all the other 
planets. It is therefore variable, and this produces 
a variation in the tropical year, which is dependent 
on the place of the equinox. The tropical year is 
actually above 4". 21 shorter than it was in the time 
of Hipparchus. This absence of the most essential 
requisite for a standard, viz. invariability, renders 
it necessary, since we cannot help employing the 
tropical year in our reckoning of time, to adopt an 
arbitrary or artificial value for it so near the truth 
as not to admit of the accumulation of its error for 
several centuries producing any practical mischief, 
and thus satisfying the ordinary wants of civil life, 
while, for scientific purposes, the tropical year, so 



268 



WONDERS OF THE HEAVENS 



adopted, is considered only as the representative 
of a certain number of integer days and a fraction, 
the day being, in effect, the only standard employ- 
ed. The case is nearly analogous to the reckoning 
of value by guineas and shillings, an artificial rela- 
tion of the two coins being fixed by law, near to, 
but scarcely ever exactly coincident with, the natu- 
ral one, determined by the relative market price 
of gold and silver, of which either the one or the 
other, whichever is really the most invariable, or 
the most in use with other nations, may be assumed 
as the true theoretical standard of value. 

The other inconvenience of the standards in 
question is their incommensurability. In our mea- 
sure of space, all our subdivisions are into aliquot 
parts : a yard is three feet, a mile eight furlongs, 
&c. But a year is no exact number of days, nor 
an integer number with any exact fraction (as one 
third or one fourth) over and above; but the sur- 
plus is an incommensurable fraction, composed of 
hours, minutes, seconds, &.C., which produces the 
same kind of inconvenience in the reckoning of 
time that it would do in that of money if we had 
gold coins of the value of twenty-one shillings, with 
odd pence and farthings, and a fraction of a farthing 
over. For this, however, there is no remedy but 
to keep a strict register of the surplus fractions, 
and, when they amount to a whole day, cast them 
over into the integer account. 

To do this in the simplest and most convenient 
manner is the object of a well-adjusted calendar. 
In the Gregorian calendar, which we follow, it is 
accomplished with remarkable simplicity and neat- 
ness by carrying a little farther than is done above 
the principle of an assumed or artificial year, and 
adopting tivo such years, both consisting of an 
exact integer number of days, (viz. one of three 
hundred and sixty-five, and the other of three hun- 
dred and sixty-six,) and laying down a simple and 
easily-remembered rule for the order in which these 
years shall succeed each other in the civil reckon- 
ing of time, so that during the lapse of at least some 
thousands of years the sum of the integer artificial 
or Gregorian years elapsed shall not differ from 
the same number of real tropical years by a whole 



day. By this contrivance, the equinoxes and sol- 
stices will always fall on days similarly situated 
and bearing the same name in each Gregorian 
year, and the seasons will forever correspond to 
the same months, instead of running the round of 
the whole year, as they must do upon any other 
system of reckoning, and used, in fact, to do before 
this was adopted. 

The Gregorian rule is as follows: — The years 
are denominated from the birth of Christ, according 
to one chronological determination of that event. 
Every year whose number is not divisible by four 
without a remainder consists of 365 days ; every 
year which is so divisible, but is not divisible by 
100, of 366; every year divisible by 100, but not 
by 400, again of 365 ; and every year divisible by 
400, again of 366. For example, the year 1837, 
not being divisible by four, consists of 365 days ; 
1840 of 366 ; 1800 and 1900 of 365 each ; but 2000 
of 366. In order to see how near this rule will 
bring us to the truth, let us see what number of 
days 10000 Gregorian years will contain, beginning 
with the year one. Now, in 10000 the numbers 
not divisible by four will be three-fourths of 10000, 
or 7500 ; those divisible by 100, but not by 400, 
will in like manner be three-fourths of 100, or 75; 
so that, in the 10000 years in question, 7575 con- 
sist of 365, and the remaining 2425 of 366, 
producing in all 3652425 days, which would give 
for an average of each year, one with another, 
365^2425. The actual value of the tropical year 
reduced into a decimal fraction is 365.24224; so 
the error of the Gregorian rule on 10000 of the 
present tropical years is 2.6, or 2*^ 14*" 24™, that is 
to say, less than a day in 3000 years, which is 
more than sufficient for all human purposes, those 
of the astronomer excepted, who is in no danger of 
being led into error from this cause. Even this 
error might be avoided by extending the wording 
of the Gregorian rule one step farther than its 
contrivers probably thought it worth while to go, 
and declaring that years divisible by 4000 should 
consist of 365 days. This would take off two in- 
teger days from the above-calculated number, and 
2.5 from a larger average, making the sum of days 



WONDERS OF THE HEAVENS 



269 



in 100000 Gregorian years 36524225, which differs 
only by a single day from 100000 real tropical 
years, such as they exist at present. 

As any distance along a high road might, though 
in a rather inconvenient and roundabout way, be 
expressed, without introducing error, by setting up 
a series of milestones at intervals of unequal 
lengths, so that every fourth mile, for instance, 
should be a yard longer than the rest, or according 
to any other fixed rule, taking care only to mark 
the stones so as to leave room for no mistake, and 
to advertise all travellers of the difference of lengths 
and their order of succession, so may any interval 
of time be expressed correctly by stating in what 
Gregorian years it begins and ends, and whereabouts 
in each. For this statement, coupled with the 
declaratory rule, enables us to say how many inte- 
ger years are to be reckoned at 365, and how many 
at 366 days. The latter years are called bissex- 
tiles, or leap-years, and the surplus days thus 
thrown into the reckoning are called intercalary or 
leap days. 

The arrangement of their calendar was a subject 
with which the astronomers of Greece were occu- 
pied, with various success, during several centuries. 
The difficulties arose from the perseverance with 
which they attempted to conciliate the motions of 
the sun and moon. The month being determined 
by a lunar, and the year by a solar revolution, 
they must soon have perceived that the former was 
not contained any integral number of times in the 
latter. Their object, then, was to find a number 
of years, or period, at the end of which a restitution 
would be effected, and the beginning of the month 
and the year again correspond. This problem was 
more difficult than they seem to have imagined; 
for, in the first place, the two revolutions are, strict- 
ly speaking, incommensurable, and, secondly, the 
moon's mean motion is subject to a secular accele- 
ration, which, even if an accurate period could be 
found, would, in the course of time, render it in- 
exact. However, it was not impossible to find some 
practical solution which would be tolerably accu- 
rate for a time of no very great length, and to this 
object their attention was directed. 



The first period of the kind alluded to was one 
of eight years, proposed by Cleostratus of Tenedos. 
To understand its advantages and defects it is 
necessary to observe that the Greek lunar year was 
composed of three hundred and fifty-four days, 
divided into twelve months, alternately of twenty- 
nine and thirty days. Cleostratus proposed in the 
course of the eight years to insert three intercalary 
months, of thirty days each, at the end of the 
third, fifth, and eighth years respectively. He thus 
had a period of 2922 days, comprising ninety-nine 
lunar revolutions. But, in reality, ninety-nine 
lunar revolutions are performed in somewhat more 
than 2923 days and 12 hours, so that at the end of 
the period there was an error of thirty-six hours on 
the place of the moon. 

Various methods were proposed to rectify this 
defect, but none with much success till we come to 
the time of Meton. This astronomer immortalized 
himself by the invention of a new cycle, which, 
taking into account its accuracy compared with 
the number of years contained in the period, may 
be considered as the most perfect ever proposed ; 
for it is clear that it is one of the great merits of a 
cycle of this kind, intended for the purposes of civil 
life, to comprise as small a number of years as pos- 
sible. The cycle of Meton was composed of nine- 
teen lunar years, in which seven months of thirty 
days were intercalated, namely, in the third, sixth, 
eighth, eleventh, fourteenth, seventeenth, and nine- 
teenth years. Besides this, some alteration was 
made in the distribution of the ordinary months: 
instead of having them alternately of twenty-nine 
and thirty days, there were one hundred and ten 
only of the former, and one hundred and twenty- 
five of the latter, in the period. To judge of the 
accuracy of the Metonian cycle, we must consider 
that nineteen solar years comprise very nearly 
6939 days, 14 hours, 25 minutes, and two hundred 
and thirty-five lunar revolutions comprise 6939 
days, 16* hours nearly, so that at the end of this 
time the moon was only about two hours behind 
the sun. The cycle of Meton comprising 6940 
days, after one period the sun had already com- 
menced his revolution nine hours and a half, the 



270 



WONDERS OF THE HEAVENS 



moon seven hours and a half. The great accuracy 
and convenience of this invention procured it uni- 
versal approbation. It was adopted throughout 
Greece, and obtained the name, which it still bears, 
of the golden number. The first cycle began in 
the year 422 B. C. 

Callippus, about a century later, proposed to 
remedy the slight defect of the cycle of Meton by 
subtracting one day every seventy-six years. This 
was done by changing, after four periods of nineteen 
years, one of the months of thirty days into one 
of twenty-nine. Callippus thus had a period of 
seventy-six years, comprising 27759 days. Now 
we may estimate that nine hundred and forty revo- 
lutions of the moon make 27758^ IS'' 6'"; seventy- 
six revolutions of the sun 27758'* 9*^ 42". The 
error on the place of the moon then was 5*^ 54"" ; on 
the sun M*" 18™. It was the accumulation of this 
error that entailed the necessity of the Gregorian 
reform. 

Hipparchus appears to have composed one of four 
Callippic periods, or three hundred and four years, 
at the end of which he subtracted a day. By refer- 
ence to what has been said, it will be seen that 
this will almost destroy any error on the moon's 
place, though it will leave one of more than a day 
on that of the sun. However, this period never 
seems to have been much used even among astron- 
omers. Ptolemy, though a follower and admirer of 
Hipparchus, employs in preference that of Cal- 
lippus. 

If the Gregorian rule, as above stated, had al- 
ways been adhered to, nothing would be easier 
than to reckon the number of days elapsed between 
the present time and any historical recorded event. 
But this is not the case, and the history of the 
calendar, with reference to chronology, or to the 
calculation of ancient observations, may be com- 
pared to that of a clock, going regularly when left 
to itself, but sometimes forgotten to be wound up, 
and, when wound, sometimes set forward, some- 
times backward, and that often to serve particular 
purposes and private interests. Such, at least, 
appears to have been the case with the Roman 
calendar (in which our own originates) from the 



time of Numa to that of Julius Caesar, when the 
lunar year of thirteen months, or three hundred 
and fifty-five days, was augmented at pleasure to 
correspond to the solar (by which the seasons are 
determined) by the arbitrary intercalations of the 
priests, and the usurpations of the decemvirs and 
other magistrates, till the confusion became inex- 
tricable. An important change took place in the 
forty-fifth year before Christ, which was the first 
regular year commencing on the 1st of January, 
being the day of the new moon immediately follow- 
ing the winter solstice of the year before. We 
may judge of the state into which the reckoning 
of time had fallen by the fact, that, to introduce 
the new system, it was necessary to enact that the 
previous year (46 B. C.) should consist of four 
hundred and fifty-five days, a circumstance which 
obtained for it the epithet of "the year of confu- 
sion." 

When Julius Caesar, and his adviser Sosigenes, 
determined that, in the Roman calendar, every 
fourth year should be bissextile, they seem to have 
supposed the year to have been composed of exact- 
ly 365 days and 6 hours. Yet Hipparchus had 
proved, a century before, that this value was about 
five minutes too great, and even his determination 
was considerably in excess, as the real length was 
not more than 365 days, 5 hours, 48 minutes, and 
45 seconds, and consequently the excess of the 
Julian above the tropical year amounted to more 
than eleven minutes. At the end of a century the 
difference had accumulated to more than eighteen 
hours, and at the end of fifteen centuries to nearly 
eleven days, by which the seasons had moved from 
the places in which they were originally fixed. 
Thus, the vernal equinox, which, at the institution 
of the calendar by Julius Caesar, fell on the 21st 
of March, had retrograded to the 10th, and, if no 
steps had been taken to correct this, in the course 
of time spring would have commenced in December, 
summer in March, autumn in June, and winter in 
September. In process of time, the equinox, 
having passed successively through all the interme- 
diate months, would have returned again to that 
of March. But before this took place a great many 



WONDERS OF THE HEAVENS. 



271 



centuries would have elapsed, and, even supposing 
the derangement to have been much more rapid, it 
may be questioned whether it would have caused 
any practical inconvenience. The ancient Egyp- 
tians knew that the solar year comprised about 
365 days and a quarter, yet they made their civil 
year of 365 days only; the consequence of which 
was that each month corresponded in succession 
to different seasons, a complete restitution being 
effected in about 1461 years. It is probable that 
the principal motive which induced many well- 
informed men, in the sixteenth century, to urge a 
reformation of the calendar, was a desire to fix in a 
more correct way the day on which the festival of 
Easter ought to be celebrated. This celebration 
having been connected with the equinox by a 
decree of the council of Nice, it became of impor- 
tance to the church to fix definitely the place of 
the equinox in the calendar. A proof that religious 
and not civil considerations led to the reform may 
be found in the extent of the changes effected. It 
may be said that a certain degree of inconvenience 
would result to the public from having a movable 
instead of a fixed year ; and though, in the Julian 
system, the anticipation of the seasons is so slow 
that the inconvenience must be nearly inapprecia- 
ble, yet there could have been no objection to 
fixing permanently the different seasons, as it might 
have been effected without difficulty by adopting a 
different intercalation for the future. But, on the 
other hand, the time at which the year shall be 
made to begin is entirely arbitrary, and in practice 
a matter of perfect indifference. In the age of 
Caesar, the year began a few days after the winter 
solstice, and the vernal equinox fell on the 21st 
of March. In the age of pope Gregory XIII., this 
equinox fell on the 10th. Here it might have been 
fixed for the future without any inconvenience ; but 
the Pope and his astronomers took the very un- 
necessary step of suppressing altogether eleven 
days in the year 1582, in order to bring the equinox 
to the 21st. This uncalled-for measure had the 
inconvenience of introducing into Europe two styles 
or modes of reckoning dates, as the new calendar 
was for a long time rejected by the Protestant 



states of Europe, and to this day has not been re- 
ceived in the empire of Russia. In the north of 
Germany it was not admitted till the year 1699, 
nor in England till 1751, one hundred and sixty- 
nine years after its publication by Gregory at Rome. 

The equinox being once brought to the 21st of 
March, the object of those who effected the reform 
was to keep it as nearly as possible to that day by 
a proper system of intercalation, and to effect this 
the Julian calendar was modified as before stated. 

It is a singular fact that the Persians have been 
for several centuries in possession of a calendar 
constructed on much more scientific principles, than 
Europe, with her superior knowledge, can boast of 
It has been stated, by La Place, Montucla, and 
. Bailly, that the Persian intercalation consisted in the 
insertion of eight days in thirty-three years. This, 
if true, would at once be a much more accurate and 
simple method than the Gregorian ; but the fact is, 
that the Persians combine two periods, each of 
considerable accuracy, the one erring a little in 
excess, the other in defect. The first period is one 
of twenty-nine years, in which they intercalate 
seven days. This is followed by four successive 
periods of thirty-three years, in each of which they 
intercalate eight times, forming a whole period of 
161 years, which includes thirty-nine intercalary 
days. To show the extreme accuracy of this 
method, it is only necessary to remark that it 
supposes the length of the year to be 365'^ S** 48"" 
49M875, the real length being 365^ 5^8" 49^7. 
The difference is less than a second, while in the 
Gregorian calendar it amounts to more than 
twenty-one seconds. The first year of the Persian 
era began with the vernal equinox, A. D. 1070. 
The astronomers of that country have very wisely 
avoided subjecting themselves to the unnecessary 
and embarrassing condition that the equinox should 
always coincide with the first day of the year. 
However, in their system it never can be far from 
it, while in the Gregorian the real equinox, which 
ought to fall on the 21st of March, may sometimes 
fall on the 19th. There can then be little doubt 
that the Persian system is the most elegant and 
scientific of any that has hitherto been used. 



aawscagHgMtr»-j«»c«gi nqffga 



272 



WONDERS OF THE HEAVENS 



The principal objection to it is, that the intercala- 
tions cannot follow a law so simple as those in the 
Gregorian calendar. On the other hand, it surpasses 
the latter in accuracy, as it does that adopted 
during the revolution in France, by being freed 
from the extreme complication consequent on 
making the beginning of the year invariably 
coincide with the equinox. 

It is fortunate for astronomy that the confusion 
of dates, and the irreconcilable contradictions which 
historical statements too often exhibit when con- 
fronted with the best knowledge we possess of the 
ancient reckonings of time, affect recorded observa- 
tions but little. An astronomical observation of 
any striking and well-marked phenomenon, carries 
with it, in most cases, abundant means of recover- 
ing its exact date when any tolerable approxima- 
tion is afforded to it by chronological records, and, 
so far from being abjectly dependent on the obscure 
and often contradictory dates which the comparison 
of ancient authorities indicates, is often itself the 
surest and most convincing evidence on which a 
chronological epoch can be brought to rest. 
Remarkable eclipses, for instance, now that the 
lunar theory is thoroughly understood, can be 
calculated back for several thousands of years 
without the possibility of mistaking the day of their 
occurrence ; and whenever any such eclipse is so 
interwoven with the account given by an ancient 
author of some historical event as to indicate pre- 
cisely the interval of time between the eclipse and 
the event, and at the same time completely to 
identify the eclipse, that date is recovered and 
lixed forever. 

The days thus parcelled out into years, the 
next step to a perfect knowledge of time is to 
secure the identification of each day by imposing 
on it a name universally known and employed. 
Since, however, the days of a whole year are too 
numerous to admit of loading the memory with 
distinct names for each, all nations have felt the 
necessity of breaking them down into parcels of a 
more moderate extent, giving names to each of 
these parcels, and particularizing the days in each 
by numbers, or by some especial indication. The 



lunar month has been resorted to in many 
instances, and some nations have, in fact, preferred 
a lunar to a solar chronology altogether, as the 
Turks and Jews continue to do to this day, making 
the year consist of thirteen lunar months, or three 
hundred and fifty-five days. Our own division into 
twelve unequal months is entirely arbitrary, and 
often productive of confusion, owing to the equi- 
voque between the lunar and calendar month. The 
intercalary day naturally attaches itself to February 
as the shortest. 

The first month of the Jewish year fell, according 
to the moon, in our August and September, the 
second in September and October, and so on. 
The first month of the Egyptian year began on the 
18th of our August. The first month of the Arabic 
and Turkish year began the 6th of July. The first 
month of the Grecian year fell, according to the 
moon, in June and July, the second in July and 
August. 

A month is divided into four parts called weeks, 
and a week into seven parts called days, so that in 
a Julian year there are thirteen such months, or 
fifty-two weeks, and one day over. The ancients 
gave the names of the sun, moon, and planets to 
the days of the week : To the first, the name of 
the sun; to the second, of the moon; to the third, 
of Mars; to the fourth, of Mercury; to the fifth, of 
Jupiter; to the sixth, of Venus; and to the seventh, 
of Saturn. 

A day is either natural or artificial. The natural 
day contains twenty-four hours : the artificial day 
is the time from sunrise to sunset. The natural 
day is either astronomical or civil. The astronom- 
ical day begins at noon, because the increase and 
decrease of days terminated by the horizon are 
very unequal among themselves, and this inequality 
is augmented by the inconstancy of the horizontal 
refractions ; therefore the astronomer takes the 
meridian for the limit of diurnal revolutions, 
reckoning noon (that is, the instant when the sun's 
centre is on the meridian) for the beginning of the 
day. The Americans, British, French, Dutch, 
Germans, Spaniards, Portuguese, and Egyptians 
begin the civil day at midnight ; the ancient 



r? 



WONDERS OF THE HEAVENS 



273 



Greeks, Jews, Bohemians, Silesians, with the 
modern Italians and Chinese, at sunset; the 
ancient Babylonians, Persians, Syrians, with the 
modern Greeks, at sunrise. 

An hour is a certain determinate part of the day, 
and is either equal or unequal. An equal hour is 
the twenty-fourth part of a mean natural day, as 
shown by well-regulated clocks and watches ; but 
these hours are not quite equal as measured by the 
returns of the sun to the meridian, because of the 
obliquity of the ecliptic and sun's unequal motion 
in it. Unequal hours are those by which the 
artificial day is divided into twelve parts, and the 
night into as many. 

An hour is divided into sixty equal parts called 
minutes, a minute into sixty equal parts called 
seconds, and these again into sixty equal parts 
called thirds. The Jews, Chaldeans, and Arabians 
divide the hour into ten hundred and eighty equal 
parts called scruples, — a number which contains 
eighteen times sixty, so that one minute contains 
eighteen scruples. 

A cycle is a perpetual round, or circulation of 
the same parts of time of any sort. The cycle of 
the sun is a revolution of twenty-eight years, in 
which time the days of the months return again to 
the same days of the week, the sun's place to the 
same signs and degrees of the ecliptic on the same 
months and days so as not to differ one degree in 
one hundred years, and the leap-years begin the 
same course over again with respect to the days of 
the week on which the days of the months fall. The 
cycle of the moon, commonly called the golden number, 
is a revolution of nineteen years, in which time 
the conjunctions, oppositions, and other aspects of 
the moon are within an hour and a half of being 
the same as they were on the same days of the 
months nineteen years before. The indiction is a 
revolution of fifteen years, used only by the 
Romans for indicating the times of certain pay- 
ments made by the subjects to that republic. It 
was established by Constantine, A. D. 312. 

Our Savior's birth, according to the common era, 

was in the 9th year of the solar cycle, and the 1st 

year of the lunar cycle ; and the 312th year after 

35 



his birth was the first year of the Roman indiction. 
Therefore, to find the year of the solar cycle, add 
nine to any given year of Christ, and divide the 
sum by twenty-eight ; the quotient is the number 
of cycles elapsed since his birth, and the remainder 
is the cycle for the given year ; if nothing remains, 
the cycle is twenty-eight. To find the lunar cycle, 
add one to the given year of Christ, and divide the 
sum by nineteen; the quotient is the number of 
cycles elapsed in the interval, and the remainder is 
the cycle for the given year ; if nothing remains, 
the cycle is nineteen. Lastly, subtract three 
hundred and twelve from the given year of Christ, 
and divide the remainder by fifteen, and what 
remains after this division is the indiction for the 
given year; if nothing remains, the indiction is 
fifteen. 

The cycle of Easter, also called the Dionysian 
period, is a revolution of five hundred and thirty- 
two years, found by multiplying the solar cycle 
twenty-eight by the lunar cycle nineteen. If the 
new moons did not anticipate upon this cycle, 
Easter-day would always be the Sunday next after 
the first full moon that follows the 21st of March; 
but, on account of the anticipation, to which no 
proper regard was had before the alteration of the 
style, the ecclesiastic Easter was several times a 
week different from the true Easter. This incon- 
venience is now remedied by making the table 
in the Common Prayer Book, which used to find 
Easter forever, of no longer use than the lunar 
difference from the new style will admit of 

The earliest Easter possible is the 22d of March, 
the latest the 25th of April. Within these limits 
are thirty-five days, and the number belonging to 
each of them is called the number of direction, 
•tecause thereby the time of Easter is found for 
any given year. 

The first seven letters of the alphabet are 
commonly placed in the almanacks to show on 
what days of the week the days of the months fall 
throughout the year ; and because one of those 
seven letters must necessarily stand against Sunday, 
it is printed in a capital form,, and called the 
Dominical letter, the other six being inserted in 



T- 



274 



WONDERS OF THE HEAVENS 



small characters to denote the other six days of 
the week. Now, since a common Julian year 
contains three hundred and sixty-five days, if this 
number be divided by seven (the number of days 
in a week) there will remain one day. If there had 
been no remainder, it is plain that the year would 
constantly begin on the same day of the week ; 
but since one remains, it is as plain that the year 
must begin and end on the same day of the week, 
and therefore the next year will begin on the day 
following. Hence, when January begins on Sunday, 
A is the Dominical or Sunday letter for that year ; 
then, because the next year begins on Monday, the 
Sunday will fall on the seventh day, to which is 
annexed the seventh letter G, which, therefore, will 
be the Dominical letter for all that year; and, as 
the third year will begin on Tuesday, the Sunday 
will fall on the sixth day, and therefore F will be the 
Sunday letter for that year; — whence it is evident 
that the Sunday letters will go annually in a 
retrograde order thus, G, F, E, D, C, B, A. In 
the course of seven years, if they were all common 
ones, the same days of the week and Dominical 
letters would return to the same days of the 
months ; but because there are three hundred and 
sixty-six days in a leap-year, if this number be 
divided by seven, there will remain two days over 
and above the fifty-two weeks of which the year 
consists, and, therefore, if the leap-year begins 
on Sunday, it will end on Monday, and the next 
year will begin on Tuesday, its first Sunday falling 
on the 6th of January, to which is annexed the 
letter F, and not G, as in common years. By this 
means, the leap-year returning every fourth year, 
the order of the Dominical letters is interrupted, 
and the series cannot return to its first state till 
after four times seven, or twenty-eight years, and 
then the same days of the months return in order 
to the same days of the week as before. 

From the multiplication of the solar cycle of 
twenty-eight years into the lunar cycle of nineteen 
years and the Roman indiction of fifteen years, 
arises the great Julian period, consisting of 7980 
years, which had its beginning 764 years before 
Strauch's supposed year of the creation, (for no 



later could all the three cycles begin together,) and 
it is not yet completed, and therefore it includes 
all other cycles, periods, and eras. There is but 
one year in the whole period that has the same 
numbers for the three cycles of which it is made 
up, and, therefore, if historians had remarked in 
their writings the cycles of each year, there would 
have been no dispute about the time of any action 
recorded by them. 

The Dionysian or common era of Christ's birth 
was about the end of the year of the Julian period 
4713, and consequently the first year of his age, 
according to that account, was the 4714th year of 
the said period. Therefore, if to the current year 
of Christ we add 4713, the sum will be the year of 
the Julian period : so the year 1837 will be found 
to be the 6550th year of that period. Or, to find 
the year of the Julian period answering to any 
given year before the first year of Christ, subtract 
the number of that given year from 4714, and the 
remainder will be the year of the Julian period. 
Thus, the year 585 before the first year of Christ 
(which was the 584th before his birth) was the 
4129th year of the said period. Lastly, to find the 
cycles of the sun, moon, and indiction for any given 
year of this period, divide the given year by twenty- 
eight, nineteen, and fifteen ; the three remainders 
will be the cycles sought, and the quotients the 
numbers of cycles run since the beginning of the 
period. So in the above 4714th year of the Julian 
period, the cycle of the sun was ten, the cycle of 
the moon two, and the cycle of indiction four, the 
solar cycle having run through 168 courses, the 
lunar 248, and the indiction 314. 

The common era of Christ's birth was not settled 
till the year 527, when Dionysius Exiguus, a Ro- 
man abbot, fixed it, as above stated, at the end of 
the 4713th year of the Julian period. This was 
four years too late, for our Savior was born before 
the death of Herod, who sought to kill him as soon 
as he heard of his birth, and, according to the 
testimony of Josephus, there was an eclipse of the 
moon in the time of Herod's last illness, which 
eclipse appears, by our astronomical tables, to have 
been in the year of the Julian period 4710, March 



f« 



WONDERS OF THE HEAVENS 



275 



13th, at three hours past midnight, at Jerusalem. 
Now, as our Savior must have been born some 
months before Herod's death, since in the interval 



he was carried into Egypt, the latest time in which 
we can fix the true era of his birth is about the 
end of the 4709th year of the Julian period. 



CHAPTER IX. 



SECTION I. 

Mensuration of the earth — Standard of measure — Astronomy teaches 
how to obtain the dimensions of the globe — Richer's observations 
on the pendulum — Their consequences — Laws of the pendulum — 
Oblate form of the earth confirmed by analogy— Early attempts 
to measure the earth — Riccioli's method — Snellius — Norwood — 
and others — Opposite theories of Newton and Huygeus — Mauper- 
tuis measures a degree in Sweden, and Oodin in Peru — Result 
— Explanation of the method of measuring the earth. 

To measure the earth, and thence to determine its 
magnitude and figure, is one of the most astonishing 
enterprises that was ever undertaken. Confined 
to a particular spot, without any other scale or 
model than his own proper dimensions, how is man 
to find the distances of places which he can never 
visit, and to embrace the circumference of the 
globe ? The space he has passed through may be 
estimated by the number of steps he has taken, 
and this will furnish him with some of the most 
simple measures, such as the foot and yard. The 
cubit is the length of his arm from the elbow to 
the tip of his middle finger, and the fathom or 
toise is his height, or the distance he can reach 
with his arms extended. But what are these small 
measures in comparison to the perimeter of the 
earth ? Instead of being confounded by the inade- 
quacy of his natural powers, man finds a resource 
in his intelligence which supplies their defect. He 
multiplies small measures till he arrives at the 
greatest, and forms to himself a unit to which he 
refers all the parts of the universe. 

By means of cords or chains, which are certain 
multiples of the toise or the yard, he obtains an 
artificial measure more convenient than the natural 
one, and with this new standard, repeated a cer- 
tain number of times in the same manner as before, 



he forms furlongs, miles, and leagues, and under- 
takes to measure such distances as would otherwise 
be indeterminable. But if it were required to 
trace the whole circumference of the earth in order 
to obtain its measure, the thing would be impos- 
sible. Mountains, rivers, and seas would be per- 
petual obstacles in the way, and uninhabitable 
climates would put a stop to our progress. In 
order to surmount these difficulties we must have 
recourse to astronomy, which furnishes a method 
of measuring the whole globe by ascertaining the 
length of a small arc of one of its great circles. 

A little before the discovery of America, the 
notion of the earth's having a globular form was 
treated by many as an impious absurdity. The 
voyage of Columbus restored to the earth its 
spherical figure, and the belief became general 
that it was a perfect globe, and the observed sim- 
plicity of nature seems to favor this idea. It how- 
ever proved to be false. Richer, in a voyage made 
to Cayenne, among other observations found that 
the pendulum of his clock no longer vibrated so 
frequently as it had done at Paris. It was neces- 
sary to shorten it considerably in order to make it 
agree with the times of the stars' passages over 
the meridian. 

Who could have believed, that, from an observa- 
tion so trifling in appearance, there should have 
originated so sublime and philosophic a truth ! A 
pendulum, like any other falling body, is acted 
upon by the force of gravity, and, in consequence 
of Richer's discovery, it was observed, that, since 
the gravity of bodies is the less powerful the farther 
they are removed fi-om the centre of the earth, the 
region of the equator must be more elevated than 



276 



WONDERS OF THE HEAVENS. 



that of France, and therefore the figure of the 
earth cannot be a sphere. 

The most intense summer heat will lengthen an 
iron rod of thirty feet long only about the eleventh 
part of an inch ; but the alteration in a pendulum 
rod of little more than three feet long was found to 
be nearly twice as great as this. It was therefore 
evident that the variation must have been owing to 
some other cause. This was confirmed by the 
French academicians in the expedition to Peru. 
They inform us, that, about Quito, at a time when it 
froze, they were obliged to shorten the pendulum for 
seconds about a sixth part of an inch. The same 
phenomenon has been frequently observed at vari- 
ous places, and it was found in all that the altera- 
tion was greater the nearer they were to the 
equator. This being the case, we can no longer 
hesitate in believing it to be caused by an actual 
diminution of gravity in those places where the ex- 
periment was made. This discovery, trifling as it 
may seem, opened a new field of speculation, and 
there are, perhaps, few facts in the circle of the 
sciences from which so many curious and useful 
consequences have been derived. 

Newton and Huygens seized the new truth with 
avidity, and, by following it through all its conse- 
quences, obtained the solution of a problem that 
seemed beyond the reach of human abilities. This 
was the determination of the figure of the earth, 
which they discovered from mathematical conside- 
rations only. 

It is a property of the pendulum that all its 
vibrations, when made in small arcs at the same 
place, are performed in the same sensible time, and 
that the periods in which each vibration is perform- 
ed is proportional to the square root of the length 
of the rod. Thus in the latitude of fifty-two degrees 
a pendulum of thirty-nine inches and an eighth in 
length makes its vibrations in a second, and one 
of about nine inches and three quarters makes its 
vibrations in half a second, so that the shorter the 
pendulum the swifter it moves. 

But the time also depends on the intensity of the 
force which impels the pendulum toward the centre 
of the earth. If this force be diminished, the body. 



having a less tendency to motion, will employ a 
longer time to move through the same space, and, 
therefore, in order that each vibration may be made 
in the same time as it was before, the rod must be 
shortened. This was the case at Cayenne. It was 
necessary to shorten the rods of the pendulums to 
make them perform their vibrations in the same 
time as at Paris. But what is the cause that ren- 
ders gravity less powerful under the equator than 
at Paris ? The diurnal rotation of the earth is 
performed round an imaginary line which passes 
through the poles, and, as the equator is farther 
from this axis of motion than any parallel circle, it 
is evident that those parts which lie under the 
equator will move with a greater velocity than 
those which are nearer the poles, and of course 
the equatorial will become more elevated than the 
polar regions, so that if the entire earth were a 
fluid, and this fluid met with no obstacles in its 
progress, it would flow from the poles toward the 
equator until an equilibrium was produced. 

This tendency of bodies to fly from the centre 
(which was spoken of in a former section) may be 
made evident in various ways. When a stone is 
whirled round swiftly by means of a sling, the arm 
finds itself stretched by a force that is exerted 
upon it by the stone in its endeavors to recede from 
the centre, and if the stone be suddenly disengaged 
from the sling, it will immediately manifest the ten- 
dency which it has to leave this constrained circular 
motion by flying off" in a straight line. Again, 
suppose a car on a railroad, moving in a right line, 
should arrive at a curve of small radius; the ten- 
dency of the car would be to proceed straight on- 
ward, but the flanges of the wheel detain it on the 
track, and, provided the propelling force be not too 
great, nor the flanges weak, it will follow the curve 
of the road. But suppose the velocity of the car 
excessive, or the flanges incapable of sustaining the 
pressure upon them ; then the wheels will be lifted 
from the track, or the flanges be broken, and the car 
will manifest its centrifugal tendency by leaving its 
constrained orbit, and moving on in the direction 
of a tangent to the curve of the road, i. e. it will 
run off" the track. Now this tendency to proceed 



WONDERS OF THE HEAVENS 



277 



onward in a right line has been imparted to all the 
heavenly bodies ; no one can explain how ; we be- 
lieve by divine impulse. But the centripetal force, 
(represented in the example of the sling by the 
thong, and in that of the car by the flanges of the 
Avheels,) that is, the force of gravity, tends to make 
these bodies rush to their centres of motion — the 
secondaries to their primary, the primaries to the 
sun. The same tendency which the moon has to the 
earth, and the earth to the sun, exists in all bodies 
near the earth to fall towards its centre, and the 
same tendency to fly off" exists in them : between 
these two tendencies we have a constant rotation 
of all of them around the earth's axis. The nearer 
a body is to the axis of motion, the more strongly 
will it be drawn toward that axis, and the less will 
be the tendency to fly off", because the motion is 
less: from both these causes, then, the tendency of 
the particles would be to recede from the poles, 
and accumulate at the equator. The experiments 
of Richer, at Cayenne, seemed well accounted for 
by the variation of gravity at different parts of the 
earth's surface, occasioned by their greater or less 
distance from the axis of motion, and by the differ- 
ence of centrifugal force in different latitudes, owing 
to the various velocities in the motion of different 
parts of the earth ; on both which accounts, a dimi- 
nution of the weight of bodies must necessarily take 
place in the equatorial regions, and cause them to 
tend to the centre with less force than at places 
near the poles. This variation more particularly 
manifests itself in the vibrations of a pendulum, 
which is the instrument that first led to the dis- 
covery here spoken of, and is still the most accu- 
rate that we possess for measuring the intensity of 
gravity in different situations; for its oscillations 
being immediately accelerated or retarded by the 
slightest alteration in this force, the continual repe- 
tition of them for a sufficient length of time renders 
the minutest change obvious by means of the clock 
to which the pendulum is attached. Every part 
of the globe from the centre to the circumference 
is subject to the action of centrifugal force; and 
supposing the primitive figure of the earth to have 
been a perfect sphere, which shape we might be- 



lieve it would naturally assume from the mutual 
attraction of its parts, the constant rotation would 
change it into an oblate spheroid. This was the 
figure ascribed to it by Newton. 

Such is the wonderful connection and secret de- 
pendence of things. Nature is uniform in all her 
operations, and it is her peculiar excellence that 
she often produces the greatest effects from the 
most apparently trivial causes. 

The elliptical figure of the earth, however, is a 
mathematical truth, which is confirmed by analogy, 
for by means of a good telescope we can perceive 
that the planets Jupiter and Saturn are flattened at 
their poles. What exists in one planet is possible in 
another, and it is natural to infer the effect in the 
earth from a similar cause. But as their rotations 
are more rapid than that of the earth, so the altera- 
tions in their figure is much more considerable. 

We are assured, from the testimony of Herodotus 
and other early historians, that attempts had been 
made to discover the true figure of the earth by 
many of the most celebrated mathematicians of 
antiquity. Ptolemy, in his writings, has preserved 
the measures of several persons* who lived before 

* It is now about two thousand years since Eratosthenes attempted 
to resolve this important problem. He knew that, on the day of the 
summer solstice, the sun illumined the bottom of a well at Syene. 
At the same instant, he observed at Alexandria that the sun was 
seven degrees and twelve minutes from the zenith, and it was sup- 
posed that Syene was due south from that place, and therefore that 

both were under the same meridian. 
Let C be the earth's centre, A Alex- 
andria, Z its zenith in the heavens, 
B Syene, and S the sun at the instant 
when it illuminated the bottom of 
the well, and consequently was in the 
zenith of that place. The angular 
measure of the celestial arc Z S, or 
the corresponding terrestrial arc AB, 
is the angle Z C S at the earth's 
centre. Eratosthenes observed the 
angle Z A S, which, by the elements 
of geometry, is less than the former 
by the angle A S C. However, this 
difference is so small that it may be altogether neglected in the 
present case, and thus the angle A C B will be nearly seven degrees 
and twelve minutes, that is, one fiftieth part of three hundred and 
sixty degrees, and consequently the arc A B of the terrestrial meridian 
one fiftieth of the earth's circumference. The distance between Alex- 
andria and Syene had been determined to be five thousand stadia : 
hence it immediately followed that the earth's circumference was two 
hundred and fifty thousand stadia. As it could not be supposed that 




278 



WONDERS OF THE HEAVENS 



the Christian era, and, from what Bailly has advanc- 
ed in his "History of Astronomy," it appears highly 
probable that this singular enterprise had been un- 
dertaken in the still more remote ages of the world. 

But as the determinations of the ancients are 
uncertain on account of our not being acquainted 
with the length of their principal measure, we shall 
pass over their peculiar methods, and proceed to 
those of the moderns, which are far more scientific. 

Riccioli, an Italian, attempted to measure the 
earth according to a method mentioned by Kepler. 
As a plumb-line tends to the centre of the earth, 
and as the distance of any two places upon the 
surface may be taken for the base of a triangle 
whose vertex is at the centre, he measured a large 
base line of this kind in the most accurate manner 
he could, and found the angles which it made with 
a plumb-line at each of its extremities. The sum 
of these angles being subtracted from one hundred 
and eighty degrees, gave him the angle at the ver- 
tex. Then it was easy, by proportion, to find the 
whole circumference. 

This method, however ingenious, is not accurate. 
He attempted to measure the earth without having 
recourse to celestial observations, an independence 
not to be attained. It is principally to the heavens 
that we are indebted for all that we know of the 
earth. Riccioli's error amounted to near six thou- 
sand toises in the length of a degree. The next 
who attempted to find the circumference of the 
earth was Snellius, a Dutchman. He measured a 
certain distance, and, by taking the celestial arc 
corresponding thereto, he found the length of a 
degree to be fifty-five thousand one hundred toises. 
His error appears to have been about two thousand 
toises in the length of a degree, most of which may 
have arisen from the use of poor instruments in 
measuring the celestial arc. 

In 1635, Norwood, an Englishman, engaged in 
the same enterprise. He took the sun's altitude 
when it was in the summer solstice both at London 
and York, and by this means found the difference 

this result was very accurate, Eratosthenes reckoned the circum- 
ference to be two hundred and fifty-two thousand stadia, which give 
in round numbers seven hundred stadia to the length of a degree. 



of latitude between these two cities to be two de- 
grees and twenty-eight minutes. He then measured 
their distance in the usual manner, and, having re- 
duced it to an arc of the meridian, he found it to 
contain twelve thousand eight hundred and forty- 
nine chains, which distance, compared with the 
difference of latitude, gave him about sixty-five 
miles to a degree. 

All the measures, however, that had been hither- 
to taken were subject to many inaccuracies. The 
means of precision, which have since been found so 
requisite to an exact investigation of this delicate 
subject, were then wanting. 

The Academy of Sciences, at Paris, perceiving 
from these and other considerations the necessity 
of a new measure of the earth, appointed Picard to 
perform this important duty, who, after immense 
labor, fixed the length of a degree at fifty-seven 
thousand and sixty toises, or about sixty-nine and a 
half English miles. 

It was afterward determined by the French king 
that the whole arc running through France should 
be measured. This great work was undertaken by 
Picard, La Hue, and Cassini, and was finished in 
the year 1718. The length of a degree was de- 
cided to be as Picard had found it by his previous 
measurement. 

These surveys had all been undertaken on the 
supposition that the earth was a perfect sphere; 
but the truth of this doctrine began to be contro- 
verted. Newton and Huygens had shown, from the 
known laws of gravitation, that the figure of the 
earth was an oblate spheroid. Cassini, on the 
other hand, depending more on the accuracy of his 
own measures than upon deductions drawn from 
theory, asserted it to be a prolate spheroid, that is, 
a sphere protuberant at the poles, and flattened at 
the equator. 

To settle this question, it was decided that a de- 
gree should be measured at or near the equator, 
and at or near the polar circle. For this purpose, 
Maupertuis and others were sent to the north oi 
Europe to measure the remotest degree they could 
reach ; Godin and others to Peru. The first 
company began their operations at Tornea, near 



WONDERS OF THE HEAVENS 



279 



the Gulf of Bothnia, on the 8th of July, 1736, and 
finished them about the 1st of June, 1737. The 
result was, that the length of a degree of the meri- 
dian near the polar circle is one hundred and seven 
thousand six hundred sixty-six and a quarter Eng- 
lish feet. The other party set off for Peru a twelve 
month earlier than their friends had for Lapland, 
yet did not finish their survey till 1741. In the 
province of Quito, they measured an arc of the 
meridian of three degrees and seven minutes, and 
the degree was found to be equal to one hundred 
and six thousand four hundred eleven and seven 
eighths English feet, being twelve hundred fifty- 
four and three eighths feet less than a degree at 
the polar circle. 

These measures afforded a complete demonstra- 
tion that the earth is flattened at the poles, and 
protuberant at the equator. For had the figure of 
it been a perfect globe, a degree of the meridian, in 
every latitude, would have been found of the same 
length ; and had the figure been that assigned by 
Cassini, a degree at the polar circle would have 
been found less than one at the equator. 

The measurement of different degrees has since 
been performed many times in different countries, 
as again in France, and also at the Cape of Good 
Hope, by La Caille ; in Italy, by Maire, Boscovich, 
and Beccaria; in Pennsylvania, by Mason and 
Dixon; in Hungary, by Liesganig; in India, by 
Lambton. 

We have heretofore spoken mostly of results ; 
we shall now proceed to give the reader some 
general idea of the method of measuring the earth 
technically called geodesic operations. The ground 
to be surveyed is divided into a series of triangles, 
at the angles of which are stations conspicuously 
visible from each other. Of these triangles, the 
angles only are measured by means of a theodolite, 
with the exception of one side of one triangle, 
which is called a base, and which is measured with 
every refinement that ingenuity can devise, or ex- 
pense command. This base is of moderate extent, 
rarely surpassing six or seven miles, and purposely 
selected in a perfectly horizontal plane, otherwise 
conveniently adapted for purposes of measurement. 



Its length between its two extreme points (which 
are dots on plates of gold or platina let into mas- 
sive blocks of stone, and which are, or at least ought 
to be, in all cases preserved with almost religious 
care as monumental records of the highest impor- 
tance) is then measured with every precaution to 
insure precision,* and its position with respect to 
the meridian, as well as the geographical positions 
of its extremities, carefully ascertained. 

The annexed figure represents such a chain of 
triangles. A B is the base, 0, C stations visible 




from both its extremities, (one of which, 0, we will 
suppose to be an observatory, with which it is an 
object that the base should be as closely and imme- 
diately connected as possible,) and D, E, F, G, H, 
K other stations, remarkable points in the country, 
by whose connection its whole surface may be 
covered, as it were, with a network of triangles. 
Now it is evident, that, the angles of the triangle 
A, B, C being observed, and one of its sides, A B, 
measured, the other two sides AC, BC may be 
calculated by the rules of trigonometry, and thus 
each of the sides A C and B C becomes in its turn 
a base capable of being employed as known sides 
of other triangles. For instance, the angles of the 
triangles A C G and B C F being known by obser- 
vation, and their sides A C and B C, we can thence 
calculate the lengths AG, C G, and B F, C F. 
Again, C G and C F being known, and the included 
angle G C F, G F may be calculated, and so on. 
Thus may all the stations be accurately determined 
and laid down, and this process may be carried on 
to any extent. 

Now, on this process there are two important 
remarks to be made. The first is, that it is neces- 

* The greatest possible error in the Irish hase of between seven and 
eight miles, near Londonderry, is supposed not to exceed two inches. 



280 



WONDERS OF THE HEAVENS. 



sary to be careful in the selection of stations, so as 
to form triangles free from any very great inequality 
in their angles. For instance, the triangle K B F 
would be a very improper one to determine the 
situation of F from observations at B and K, because 
the angle F being very acute, a small error in the 
angle K would produce a great one in the place of 
F upon the line B F. Such ill-conditioned triangles, 
therefore, must be avoided. But if this be attended 
to, the accuracy of the determination of the calcu- 
lated sides will not be much short of that which 
would be obtained by actual measurement if it were 
practicable ; and, therefore, as we recede from the 
base on all sides as a centre, it will speedily be- 
come practicable to use as bases the sides of much 
larger triangles, such as G F, G H, H K, &c., by 
which means the next step of the operation will 
come to be prosecuted on a much larger scale, and 
embrace far greater intervals, than it would have 
been safe to do (for the above reason) in the imme- 
diate neighborhood of the base. Thus it becomes 
easy to divide the whole face of a country into great 
triangles of from thirty to one hundred miles in 
their sides, according to the nature of the ground, 
which, being once well determined, may be after- 
wards, by a second series of subordinate operations, 
broken up into smaller ones, and these again into 
others of a still minuter order, till the final filling 
in is brought within the limits of personal survey 
and draftsmanship, and till a map is constructed 
with any required degree of detail. 

The next remark we have to make is, that all 
the triangles in question are not, rigorously speak- 
ing, plane, but spherical, existing on the surface of a 
sphere, or rather, to speak correctly, of an ellipsoid. 
In very small triangles, of six or seven miles in the 
side, this may be neglected, as the difference is 
imperceptible; but in the larger ones it must be 
taken into consideration. 

It is evident, that, as every object used for point- 
ing the telescope of a theodolite has some certain 
elevation, not only above the soil, but above the 
level of the sea, and as, moreover, these elevations 
differ in every instance, a reduction to the horizon of 
all the measured angles would appear to be requir- 



ed. But, in fact, by the construction of the theodo- 
lite, which is nothing more than an altitude and 
azimuth instrument, this reduction is made in the 
very act of reading off" the horizontal angles. Let 
E be the centre of the earth; A, B, C the places 
on its spherical surface to which three stations A, 




P, Q, in a country, are referred by radii E, A, 
E B P, E C Q. If a theodolite be stationed at A, 
the axis of its horizontal circle will point to E when 
truly adjusted, and its plane will be a tangent to 
the sphere at A, intersecting the radii E B P, E C Q, 
at M and N, above the spherical surface. The 
telescope of the theodolite, it is true, is pointed in 
succession to P and Q, ; but the readings off" of its 
azimuth circle give, not the angle P A Q between 
the directions of the telescope, or between the ob- 
jects P, Q, as seen from A, but the azimuthal angle 
MAN, which is the measure of the angle A of the 
spherical triangle BAG. Hence arises this re- 
markable circumstance, that the sum of the three 
observed angles of any of the great triangles in 
geodesical operations is always found to be rather 
more than one hundred and eighty degrees. Were 
the earth's surface a plane, it ought to be exactly 
one hundred and eighty degrees ; and this excess, 
which is called the spherical excess, is so far from 
being a proof of incorrectness in the work that it 
is essential to its accuracy, and offers at the same 
time another palpable proof of the earth's sphe- 
ricity. 

The true way, then, of conceiving the subject of 
a trigonometrical survey, when the spherical form 
of the earth is taken into consideration, is to regard 
the network of triangles with which the country is 
covered as the bases of an assemblage of pyramids 



WONDERS OF THE HEAVENS 



281 



converging to the centre of the earth. The the- 
odolite gives us the true measures of the angles included 
by the planes of these pyramids , and the surface of an 
imaginary sphere on the level of the sea intersects 
them in an assemblage of spherical triangles, above 
whose angles, in the radii prolonged, the real sta- 
tions of observation are raised by the superficial 
inequalities of mountain and valley. The operose 
calculations of spherical trigonometry w^hich this 
consideration would seem to render necessary for 
the reductions of a survey, are dispensed with in 
practice by a very simple and easy rule called the 
rule for the spherical excess, which is to be found in 
most works on trigonometry. If we would take 
into account the ellipticity of the earth, it may also 
be done by appropriate processes of calculation, 
which, however, are too abstruse to dwell upon in 
a work like the present. 

Whatever process of calculation we adopt, the 
result will be a reduction to the level of the sea 
of all the triangles, and the consequent determina- 
tion of the geographical latitude and longitude of 
every station observed. 



SECTION II. 

Methods of finding the moon's parallax and distance — Difficulty in 
finding the sun's parallax — Transits of Mercury and Venus — Sun's 
parallax found by the transit of Venus — The sun's distance — 
Distances of the planets — Method of finding the diameters and 
magnitudes of the sun and planets — Method of finding their masses 
and densities. 

Astronomy furnishes a variety of methods for de- 
termining the distances of the heavenly bodies ; but 
as many of them are involved in long and difficult 
calculations, we shall confine ourselves to those that 
admit of the most familiar explanation. We shall 
begin with the moon, for the method of finding the 
distance of this our neighboring planet being once 
known, it will be easy to perceive that the same 
method may be extended to the other planets. 

In the method about to be described, the first 
thing is to find the difference between the moon's 

place when it appears in the horizon to a spectator 

36 



on the earth's surface, and that which it would 
appear to occupy to a person at the earth's centre, 
or, which is the same thing, to find the apparent 
semidiameter of the earth to an observer at the 
moon's centre. This may be shown to be practi- 
cable without entering into the minutiae of the 
matter. 

For this purpose, let us suppose an observer to 
be placed upon any point A of the equator BAG 




at the time the moon is moving in the celestial 
equator D M P ; then, as the latter circle is in the 
plane of the former, the moon will pass directly 
over his head, and descend perpendicularly to the 
horizon E N. In this situation of the spectator at 
A, the moon will appear to have described a quar- 
ter of a circle, or ninety degrees, in passing from 
the zenith to the sensible horizon at N, while, to a 
spectator at 0, the centre of the earth, it would not 
appear to have described a quarter of a circle till 
it reached the rational horizon at P. 

But the moon appears to revolve round the earth 
in about twenty-four hours and forty-eight minutes. 
It will therefore revolve from M to P in six hours 
and twelve minutes; and if the time required in 
moving from M to N be found by observation, and 
subtracted from six hours and twelve minutes, the 
time of moving from M to P, the remainder will be 
the time requisite to describe the arcN P. Having 
found the measure of N P in time, it is easily con- 
verted into degrees by allowing at the rate of fifteen 



ITfwJ 



282 



WONDERS OF THE HEAVENS 



degrees to an hour. Now the angle NOP contains 
the same number of degrees as the arc N P, and 
N P is equal to A N 0. This last angle A N 
is called the moon's horizontal parallax. 

Thus, in the triangle N A, we have ang. AN 0, 
the side A equal to the semidiameter of the 
earth, and the angle A N equal to ninety de- 
grees. From these we can easily calculate the 
side N, which here represents the moon's dis- 
tance from the centre of the earth. 

But the true quantity of the moon's horizontal 
parallax cannot be accurately determined by this 
method, on account of the varying declination of 
that body, and the perpetual changes in the state 
of the atmosphere. Astronomers have therefore 
thought of the following method, which is free from 
those objections, and is sufficient for determining 
the parallax and distance of the moon with some 
degree of precision. 

Suppose two observers were placed under the 
same meridian at A and B, so distant from each 




other that the one at A sees the moon M in his 
horizon whilst the other at B sees it in his zenith. 
Now the angle at is equal to the difference of 
latitude of the two observers, the angle A is ninety 
degrees, and the side A is the semidiameter of 
the earth. These three things being given in the 
triangle A M, it will be easy to find the side M, 
the moon's distance. If the angle be subtracted 
from ninety degrees, we shall have the angle at M, 
which is the moon's horizontal parallax. We hope 
our readers will readily comprehend this, as it is 
the simplest solution the problem admits. We 
shall add a more general method by which the dis- 
tance of the moon can be determined when the 
observers are at any two distant places under the 



same meridian. Suppose the two observers were 
at the points A and B, whose distance A B, or dif- 




ference of latitude, is already known ; then measure 
the moon's distances from the zeniths Z and z at 
the moment it passes the celestial meridian 2iZ. 
The distance M of the moon may be determined 
as follows ■:■ — 

In the triangle A B 0, A and B are each equal 
to the earth's semidiameter, and the angle A B 
contains the same number of degrees as the arc 
A B, which is known. These three things being 
known, the side A B and the angles ABO and 
B A can be calculated. If the angles M A Z and 
M B 2r (which contain the same number of degrees 
as the zenith distances already measured) be sub- 
tracted from one hundred and eighty degrees, the 
remainders will be the angles 0AM and B M. 
From the angles thus found subtract the angles 
B A and ABO, (found before,) and there will 
remain the angle BAM and ABM; so that in the 
triangle A B M we have these two angles and the 
side A B ; consequently the side M B may be found. 
Now, in the triangle 0MB having the two sides 
B M and B 0, and the angle B M, we can easily 
find M, the distance of the moon from the centre 
of the earth. 

The distance of the sun from the earth might be 



WONDERS OF THE HEAVENS 



283 



determined in nearly the same manner as that of 
the moon, were not its horizontal parallax so small 
as to be scarcely perceptible ; for the angle under 
which the semidiameter of the earth appears at the 
sun does not exceed nine seconds, and as a mis- 
take of one second in so small an angle would 
occasion an error of no less than seven millions of 
miles in the distance, it may easily be perceived 
that an extraordinary degree of skill is requisite to 
surmount the difficulties attending this delicate sub- 
ject. By means of the transits of Venus over the 
sun's disc, this problem has been solved with a 
degree of precision unlooked for by the astronomers 
of ancient times. 

When Dr. Halley was at St, Helena, whither he 
went for the purpose of making a catalogue of the 
stars in the southern hemisphere, he observed a 
transit of Mercury over the sun's disc, and, by 
means of a good telescope, it appeared to him that 
he could determine the time of the ingress and 
egress without its being subject to an error of one 
second,* upon which he immediately concluded 
that the sun's parallax might be determined, by 
such observations, from the difference of the times 
of the transit over the sun at different places upon 
the earth's surface. But this difference is so small 
in Mercury that it would render the conclusion 
subject to a great degree of inaccuracy. In Venus, 
however, whose parallax is nearly four times as 
great as that of the sun, there will be a very con- 
siderable difference between the times of the tran- 
sits seen from different parts of the earth, by which 
the accuracy of the conclusion will be proportion- 
ably increased. Halley, therefore, proposed to 
determine the sun's parallax from the transit of 
Venus over the sun's disc, observed at different 
places on the earth ; and, as it was not probable 
that he himself should live to observe the next 
transits, which happened in 1761 and 1769, he 
very earnestly recommended the attention of them 

* Hence Dr. Halley concluded, that, by a transit of Venus, the 
sun's distance might be determined with certainty to the 500th part 
of the whole; but the observations upon the transits which happened 
in 1761 and 1769, showed that the time of contact of the limbs of the 
sun and Venus could not be determined with that degree of certainty. 



to the astronomers who should be alive at that 
time. Astronomers were therefore sent from Eng- 
land and France to the most proper parts of the 
earth to observe both those transits, from the result 
of which the parallax has been determined to a 
very great degree of accuracy. 

Kepler was the first person who predicted the 
transits of Venus and Mercury over the sun's disc. 
He foretold the transit of Mercury in 1631, and the 
transits of Venus in 1631 and 1761. The first 
time Venus was ever seen upon the sun was in the 
year 1639, on November 24, at Hoole, near 
Liverpool, by Horrox. He was employed in calcu- 
lating an Ephemeris from the Lansberg Tables, 
which gave, at the conjunction of Venus with the 
sun on that day, its apparent latitude less than the 
semidiameter of the sun. But as these tables had 
so often deceived him, he consulted the tables 
constructed by Kepler, according to which the 
conjunction would be at eight hours and one minute 
A. M., at Manchester, and the planet's latitude 
fourteen minutes and ten seconds south; but, from 
his own corrections, he expected it to happen at 
three hours and fifty-seven minutes P. M., with ten 
minutes south latitude. He accordingly gaA'^e this 
information to his friend Crabtree, at Manchester, 
desiring him to observe it ; and he himself also 
prepared to make observations upon it by transmit- 
ting the sun's image through a telescope into a 
dark chamber. He described a circle of about six 
inches diameter, and divided the circumference 
into three hundred and sixty degrees, and the 
diameter into one hundred and twenty equal parts, 
and caused the sun's image to fill up the circle. 
He began to observe on the 23d, and repeated his 
observations on the 24th till one o'clock, when he 
was unfortunately called away by business; but 
returning at fifteen minutes after three o'clock, he 
had the satisfaction of seeing Venus upon the sun's 
disc, just wholly entered on the left side, so that 
the limbs perfectly coincided. At thirty-five minutes 
after three, he found the distance of Venus from 
the sun's centre to be thirteen minutes and thirty 
seconds; and at forty-five minutes after three, he 
found it to be thirteen minutes. The sun setting 



284 



WONDERS OF THE HEAVENS 



at fifty minutes after three o'clock, put an end to 
his observations. From these observations, Horrox 
endeavored to correct some of the elements of the 
orbit of Venus. He found Venus had entered upon 
the disc at about sixty-two degrees and thirty 
minutes from the vertex towards the right on the 
image, which by the telescope was inverted. He 
measured the diameter of Venus, and found it to be 
to that of the sun as 1,12 : 30 as near as he could 
measure. Crabtree, on account of the clouds, got 
only one sight of Venus, which was at three hours 
and forty-five minutes. Horrox wrote a treatise 
entitled "Venus seen upon the sun," but did not 
live to publish it. It was, however, afterwards 
published by Hevelius. Gassendus observed the 
transit of Mercury which happened on November 7, 
1631, and this was the first which had ever been 
observed. He made his observations in the same 
manner that Horrox did after him. Since his time, 
several transits of Mercury have been observed, as 
they frequently happen ; whereas only two transits 
of Venus have happened since the time of Horrox. 
The transits of Venus are of very rare occurrence, 
taking place alternately at intervals of eight and 
of one hundred and thirteen years, or thereabouts. 
As astronomical phenomena, they are, however, 
extremely important, since they afford the best 
and most exact means we possess of ascertaining 
the sun's distance or its parallax. Without going 
into the niceties of calculation of this problem, 
which, owing to the great multitude of circum- 
stances to be attended to, are extremely intricate, 
we shall here explain its principle, which, in the 
abstract, is very simple and obvious. Let E be the 
earth, V Venus, and S the sun, and C D the portion 




of Venus's relative orbit which she describes while 
in the act of transiting the sun's disc. Suppose 
A B two spectators at opposite extremities of that 
diameter of the earth which is perpendicular to the 
ecliptic, and, to avoid complicating the case, let us 



lay out of consideration the earth's rotation, and 
suppose A, B to retain that situation during the 
whole time of the transit. Then, at any moment 
when the spectator at A sees the centre of Venus 
projected at a on the sun's disc, he at B will see it 
projected at b. If one or other spectator could 
then suddenly transport himself from A to B, he 
would see Venus suddenly displaced on the disc 
from a to b; and if he had any means of noting 
accurately the place of the points on the disc, 
either by micrometrical measures from its edge, or 
by other means, he might ascertain the angular 
measure of c ^ as seen from the earth. Now, since 
A V a, B V ^ are straight lines, and therefore 
make equal angles on each side of V, c 6 will be to 
A B as the distance of Venus from the sun is to its 
distance from the earth, or as sixty-eight to twenty- 
seven, or nearly as two and a half to one: ab, 
therefore, occupies on the sun's disc a space two 
and a half times as great as the earth's diameter, 
and its angular measure is therefore equal to 
about two and a half times the earth's apparent 
diameter at the distance of the sun, or, which is 
the same thing, to five times the sun's horizontal 
parallax. . Any error, therefore, which may be 
committed in measuring ab, will entail only one 
fifth of that error on the horizontal parallax con- 
cluded from it. 

The thing to be ascertained, therefore, is, in 
fact, neither more nor less than the breadth of the 
zone P Q R S, j? ^ r s, included between the extreme 
apparent paths of the centre of Venus across the 
sun's disc from its entry on one side to its quitting 
it on the other. The whole business of the 
observers at A, B, therefore, resolves itself into 
this, — to ascertain, with all possible care and 
precision, each at his own station, this path, where 
it enters, where it quits, and what segments of the 
sun's disc it cuts off. Now, one of the most exact 
ways in which (conjoined with careful micrometric 
measures) this can" be done, is by noting the time 
occupied in the whole transit; for the relative 
angular motion of Venus being, in fact, very pre- 
cisely known fi-om the tables of her motion, and 
the apparent path being very nearly a straight line. 



WONDERS OF THE HEAVENS. 



285 



these times give us a measure, on a very enlarged 
scale, of the lengths of the chords of the segments 
cut off, and the sun's diameter being known also 
with great precision, their versed sines, and there- 
fore their difference, or the breadth of the zone 
required, becomes known. To obtain these times 
correctly, each observer must ascertain the instants 
of ingress and egress of the centre. To do this, he 
must note, 1st, the instant when the first visible 
impression or notch on the edge of the disc at P is 
produced, or the first external contact; 2dly, when 
the planet is just wholly immersed, and the broken 
edge of the disc just closes again at Q, or the first 
internal contact; and, lastly, he must make the 
same observations at the egress at R, S. The 
mean of the internal and external contacts gives 
the entry and egress of the planet's centre. 

The modifications introduced into this process 
by the earth's rotation on its axis, and by other 
geographical stations of the observers thereon than 
here supposed, are similar in their principles to 
those which enter into the calculation of a solar 
eclipse, or the occultation of a star by the moon, 
only more refined. Any consideration of them 
here, however, would lead us too far ; but in the 
view we have taken of the subject, it affords an 
admirable example of the way in which minute 
elements in astronomy may become magnified in 
their effects, and, by being made subject to mea- 
surements on a greatly-enlarged scale, or by 
substituting the measure of time for space, may be 
ascertained with a degree of precision adequate to 
every purpose, by only watching favorable oppor- 
tunities, and taking advantage of nicely-adjusted 
combinations of circumstances. So important has 
this observation appeared to astronomers, that, at 
the last transit of Venus, in 1769, expeditions were 
fitted out, on the most efficient scale, by the British, 
French, Russian, and other governments to the 
remotest corners of the globe for the express 
purpose of performing it. The celebrated expedi- 
tion of captain Cook to Otaheite was one of them. 
The general result of all the observations made on 
this most memorable occasion gives 8". 5776 for 
:he sun's horizontal parallax. 



Having found the parallax of the sun from a 
transit of Venus over that luminary, the same 
method may be applied to find its distance from 
the earth as was used to find the moon's distance. 
And, as we have before stated this distance at 
mean is found to be about ninety-five millions of 
miles, — a distance so immense that a cannon ball 
(which, with a certain charge, is known to move at 
the rate of about eight miles a minute) would be 
more than twenty-two years in going from the 
earth to the sun ; and if a spectator could be 
placed in the sun, and was to look at the semi- 
diameter of the earth, this line, which is nearly 
four thousand miles in length, would appear to him 
under an angle of only eight and a half seconds. 
Consider this, and you will find it a subject worthy 
of admiration and wonder. 

The distance of the earth from the sun being 
thus found, the distance of all the rest of the 
planets may be determined by the stated laws of 
nature, — laws that have been mentioned as the 
discoveries of Kepler. Suppose, for example, we 
wished to find the distance of Saturn fi'om the 
sun ; this may be found by proportion as follows : 
As the square* of the earth's period of revolution is 
to the square of Saturn's period, so is the cubef of 
the earth's mean distance to the cube of Saturn's 
mean distance. The cube root of this last number 
being found, will be the mean distance of Saturn 
from the sun. 

In a manner equally easy may the real diam- 
eters of the sun and planets be determined from 
their apparent diameters and their distances. J 
Also, having found the real diameter of any hea- 
venly body, its magnitude may be deduced there- 
from. Thus, since the diameter of the earth is 
known to be seven thousand nine hundred and 
twelve miles, and that of the sun eight hundred and 

* A square is the product of a number by itself. Thus, four times 
four is sixteen : sixteen is the square of four. 

t A cube is the product of a number by itself twice. Thus, four 
times four is sixteen, and four times sixteen is sixty-four : sixty-four 
is the cube of four, and four is the cube root of sixty-four. 

% Thus, for example, if A B C be the sun, whose mean apparent 
diameter as seen from the earth E is thirty-two minutes and three 



286 



WONDERS OF THE HEAVENS 



eighty-two thousand miles, and as the magnitudes 
of spherical bodies are to each other as the cubes 
of their diameters, it would be seen, if we should 
compare the cube of the first number with the 
cubes of the sun's and moon's diameters, that the 
bulk of the sun is more than a million of times 
greater than that of the earth, and the bulk of the 
earth about fifty times greater than that of the 
moon. And in the same manner might the diam- 
eters and magnitudes of the other planets be 
determined, supposing their distances and apparent 
diameters already known. 

Another problem equally curious with the last, 
and apparently involved in greater obscurity, is to 
determine the comparative densities of the sun and 
planets with respect to that of the earth. When 
we consider their immense distances from us, this 
seems too great an undertaking for the limited 
powers of the human mind. But difficulties pre- 
sented to an active mind, instead of repressing its 
ardor and retarding its progress, serve only to 
stimulate it to greater exertions and nobler pur- 
suits. We have already seen by what means the 
magnitudes and distances of the planets have been 
ascertained, and we shall endeavor to render the 
present subject equally clear. For this purpose, it 
will be proper to observe, that, by the densities of 
bodies is to be understood their degree of com- 
pactness, or the greater or less quantity of matter 
that is contained in them when compared, bulk 
for bulk, with each other. According to this 
definition, the quantities of matter in bodies will be 
as their densities when their magnitudes are equal, 

seconds, and its mean distance ninety-five millions of miles, the 
proportion will be, As the sine of ninety degrees is to E P, (ninety-five 

A 




million,) so is the sine of A E P sixteen minutes and one and a half 
seconds to P A. the double of which, or A B, is the diameter of the 
sun in miles. 



and as their magnitudes when their densities are 
equal; therefore the quantities of matter in any 
two bodies are jointly as the products of their 
magnitudes and densities, and, therefore, conversely, 
the densities of bodies of difierent magnitudes may 
be expressed by their masses divided by their 
magnitudes. 

We must explain, therefore, by what means a 
knowledge of the masses of the heavenly bodies is 
obtained, since the rest may be found by common 
division. To do this, we must have recourse to 
the doctrine of gravitation, from which it is known 
that the quantity of matter in the sun and planets 
is as their attractive power at equal distances 
from their centres. If, therefore, we can ascertain 
the relative attractive powers of any two of those 
bodies, this will give their relative masses, from 
which, and their known magnitudes, their densities 
with respect to each other may be determined 
with facility. 

The ratio of this attractive power between the 
earth and sun is easily ascertained, for a body at 
the earth's surface is known to fall through sixteen 
and one twelfth feet in the first second of its descent, 
and since the spaces described at different distances 
from the centre are reciprocally as the squares of 
those distances, it is easy to compute what space a 
body would fall through in a second toward the 
earth if it were placed at the distance of the sun. 
And as the diameter of the earth's orbit is known, 
and the time of its annual revolution, we can 
ascertain the arc described by this body in a 
second, and thence how much it is deflected from 
its tangent in a second by the attractive power of 
the sun, or, which is the same, through what space 
a body would descend in one second toward the 
sun were it placed at the distance of the earth. 
Whence, going through the calculation here men- 
tioned, we shall have the spaces described by a 
body when placed at equal distances from the sun 
and earth respectively, and descending toward 
them during equal portions of time ; and since the 
spaces fallen through, in this case, are as the 
attractive powers, and the latter are as the masses 
of the attracting bodies, we have at once, by com- 



WONDERS OF THE HEAVENS 



287 



paring the spaces so described, the relative pro- 
portion of the masses of the earth and sun, and, 
by dividing their relative masses by their absolute 
magnitudes, we obtain their proportional densities. 

From this computation, it will appear that the 
density of the earth is to the density of the sun as 
four to one, and, as the density of the earth is 
known to be to the density of water as five and a 
half to one, it follows that the density of the sun 
is to that of water as one and three-eighths to one. 
We cannot, however, proceed in the same manner 
with the other planets, because we have no means 
of ascertaining their respective attractive powers 
at their surfaces ; therefore we must have recourse 
to their satellites, and compare the deflection of 
each of them from its tangent with their respective 
distances from their primaries. For example, to 
find the relative densities of the earth and Jupiter, 
we must first estimate how much the moon is 
deflected from her tangent in one second by the 
attractive power of the earth, and how much it 
would be deflected in the same time if it were 
placed at the same distance from the centre of the 
earth as any one of Jupiter's satellites is from the 
centre of that planet, which distances are all 
known from their periodic times. 

By this means, we shall have the absolute spaces 
described by two bodies, placed at the same dis- 
tances, and falling in the same time toward the 
earth and Jupiter ; and these spaces, as we have 
before seen, being as the attractive power of the 
two bodies, and the latter as their masses, it 
follows, that, by comparing, as above, the spaces 
described, we shall obtain the ratio of the masses, 
the division of which by their absolute magnitudes 
will give us their proportional densities. From 
this it will appear that the density of Jupiter is 
to that of the earth as -^-^^ to 1, being a little less 
than the density of the sun, and a little more than 
that of sea-water. 

It is obvious that the same method may be 
employed for determining the density of Saturn 
and Herschel; but those planets which have no 
satellites cannot be submitted to the same calcula- 
tion, nor would it be proper in this treatise to 



attempt to render the method used in these cases 
intelligible, as it requires a knowledge of some of 
the higher branches of mathematics. 



SECTION III. 

Nature of light unsettled — Its properties known — Refraction — Exper- 
iments illustrating refraction — Cause of twilight — Advantages 
and disadvantages of refraction — Knowledge of the atmosphere 
important to the astronomer — Amount of refraction at the zenith, 
the horizon, and at intermediate points — Explanation of the " sun 
drawing water " — Terrestrial refraction — Aberration — Bradley's 
observations — Inferences — Motion of light — Aberration confirms 
the motion of the earth in an orbit — Precession of the equinoxes — 
Nutation — Obliquity of the ecliptic — Its cause and effects. 

There is, perhaps, no subject in natural philosophy 
that has been more controverted than that relating 
to the nature of light, some considering it as a 
fluid, and others as a principle consisting in pulsa- 
tions, or vibrations, propagated from the luminous 
body through a subtle etherial medium, which 
affects the optic nerve in the same manner as sound 
affects the organ of hearing. But this uncertainty 
has not prevented astronomers from obtaining a 
knowledge of its properties. 

Light, so far as it depends on the sun's rays, 
decreases in proportion to the squares of the dis- 
tances of the planets from the sun. This is easily 
demonstrated by a figure. Let the light which 




flows fi:'om a point A, and passes through a square 
hole B, be received upon a plane C parallel to 
the plane of the hole, or let the figure C be the 
shadow of the plane B, and when the distance C 
is double of B, the length and breadth of the 
shadow C will be each double of the length and 
breadth of the plane B, and treble when A D is 
treble of A B, and so on, which may be easily 



288 



WONDERS OF THE HEAVENS 



examined by the light of a candle placed at A. 
Therefore the surface of the shadow C, at the dis- 
tance A C, (double of A B,) is divisible into four 
squares, and at a treble distance into nine squares, 
severally equal to the square B, as represented in 
the figure. The light, then, which falls upon the 
plane B, being suffered to pass to double that 
distance, will be uniformly spread over four times 
the space, and consequently will be four times 
thinner in every part of that space ; and at a treble 
distance it will be nine times thinner; and at a 
quadruple distance, sixteen times thinner than it 
was at first ; and so on, according to the increase 
of the square surfaces B, C, D, E, built upon the 
distances A B, AC, AD, A E. Consequently the 
quantities of this rarefied light received upon a 
surface, of any given size and shape whatever, 
removed successively to these several distances, 
will be but one quarter, one ninth, one sixteenth 
of the whole quantity received by it at the first 
distance A B ; or, in general words, the densities 
and quantities of light received upon any given 
plane are diminished in the same proportion as the 
squares of the distances of that plane from the 
luminous body are increased, and, on the contrary, 
are increased in the same proportion as these 
squares are diminished. 

The more a telescope magnifies the disks of the 
moon and planets, they appear so much dimmer 
than to the naked eye, because the telescope 
cannot magnify the quantity of light as it does the 
surface, and, by spreading the same quantity of 
light over a surface so much larger than the naked 
eye beheld, just so much dimmer must it appear 
when viewed by a telescope than by the naked 
eye. 

When a ray of light passes out of one medium* 
into another, it is refracted, or turned out of its 
first course, more or less as it falls more or less 
obliquely on the refracting surface which divides 
the two media. This may be proved by several 
experiments: 1st, in a basin FGH put a piece 
of money, as D B, and then retire from it, as to A, 

* Any substance through which light can pass, as water, air, glass, 
diamond, &c., is called a medium. 



till the edge of the basin at E just hides the money 
from your sight ; then, keeping your head steady, 
let another person fill the basin gently with water. 




As he fills it, you will see more and more of the 
piece D B, which will be all in view when the 
basin is full, and appear as if lifted up to C; for 
the ray A E B, which was straight whilst the basin 
was empty, is now bent at the surface of the water 
in E, and turned out of its rectilineal course into 
the direction E D ; or, in other words, the ray 
D E K, that proceeded in a straight line from the 
edge D whilst the basin was empty, and went 
above the eye at A, is now bent at E, and, instead 
of going on in the rectilineal direction DEK, goes 
in the angled direction D E A, and, by entering the 
eye at A, renders the object D B visible. 2dly, 
place the basin where the sun shines obliquely, 
and observe where the shadow of the rim E falls 
on the bottom, as at B ; then fill it with water, and 
the shadow will fall at D ; which proves that the 
rays of light falling obliquely on the surface of the 
water are refracted or bent downwards into it. 

The less obliquely the rays of light fall upon the 
surface of any medium, the less they are refracted ; 
and if they fall perpendicularly thereon, they are 
not refracted at all. In the last experiment, the 
higher the sun rises the less will be the difference 
between the places where the edge of the shadow 
falls in the empty and full basin. And, 3dly, if a 
stick be laid over the basin, and the sun's rays be 
reflected perpendicularly into it from a looking- 
glass, the shadow of the stick will fall upon the 
same place of the bottom whether the basin be 
full or empty. 

The same effects will also take place when the 
experiment is performed with any other fluid ; but 



WONDERS OF THE HEAVENS. 



289 



the denser the medium the more will the light be 
refracted in passing through it. 

From these statements, it will readily appear 
that objects can seldom be seen in their true 
places. In consequence of this property of refrac- 
tion, we enjoy the light of the sun while it is yet 
below the horizon, this being the cause that pro- 
duces the morning and evening twilight. The 
sun's rays, in falling upon the higher part of the 
atmosphere, are refracted to our eyes, forming a 
faint light, which gradually augments till it becomes 
day. It is in those brilliant colors which paint the 
clouds before the rising of the sun that the poets 
have placed Aurora, or the goddess of the morn. 
She opens the gates of day with her rosy fingers, 
and the daughter of the air and the sun has her 
throne in the atmosphere. 

Had we no atmosphere, the rays of light would 
come to us (if at all) in straight lines,* and the 
appearance and disappearance of the sun would be 
instantaneous. We should have a sudden transition 
from the brightest sunshine to the blackest dark- 
ness at sunset, and from the blackest darkness to 
an overwhelming blaze of light at sunrise. With- 
out an atmosphere, only that part of the heavens 
in which the sun was situated would be bright; 
and if we could live without air, and should turn 
our backs toward the sun, the heavens we fronted 
would appear as black as the night, and the stars 
would be as visible as now they are in the noctur- 
nal sky. How inconvenient and dangerous would 
such a state of things be to mortals constituted like 
the inhabitants of this earth! Refraction, therefore, 
is beneficial not only as it gradually prepares us 
for the light of the sun, but also as it prolongs the 
duration of the day. An ever-kind Providence 
has established these gradations to heighten our 
pleasures by variety : the scene is perpetually 
changing, but the order of things is immutable and 
eternal. 

It is the power which air possesses, in common 
with all transparent media, o^ nrfr acting the rays of 
light, or bending them out of their straight course, 

* We say " if at all," because it is probable that light is as much 
dependent on the atmosphere as on the body we call luminous. 
: "■ 37 



which renders a knowledge of the constitution 
of the atmosphere important to the astronomer. 
Owing to this property, objects seen obliquely 
through it appear otherwise situated than they 
would to the same spectator had the atmosphere 
no existence. It thus produces a false impression 
respecting their places, which must be rectified 
by ascertaining the amount and direction of the 
displacement so apparently produced on each 
before we can come at a knowledge of the true 
directions in which they are situated from us at 
any assigned moment. 

Suppose a spectator placed at A, any point of 
the earth's surface K A A;, and let L /, Mm, N w 




represent the successive strata or layers of de- 
creasing density into which we may conceive the 
atmosphere to be divided, and which are spherical 
surfaces concentric with K^, the earth's surface. 
Let S represent a star, or other heavenly body, 
beyond the utmost limit of the atmosphere; then, 
if the air were away, the spectator would see it in 
the direction of the straight line A S. But, in 
reality, when the ray of light S A reaches the atmo- 
sphere, suppose at d, it will, by the laws of optics, 
begin to bend downwards and take a more inclined 
direction, as dc. This bending will at first be 
imperceptible, owing to the extreme tenuity of the 
uppermost strata; but, as it advances downwards, 
the strata continually increasing in density, it will 
continually undergo greater and greater refraction 
in the same direction, and thus, instead of pur- 
suing the straight line SJA, it will describe a 
curve Sdcba, continually more and more concave 
downwards, and will reach the earth, not at A, 
but at a certain point a, nearer to S. This ray, 



290 



WONDERS OF THE HEAVENS 



consequently, will not reach the spectator's eye. 
The ray by which he will see the star, therefore, is 
not SdA, but another ray, which, had there been 
no atmosphere would have struck the earth at K, 
a point behind the spectator, but which, being bent 
by the air into the curve S D C B A, actually strikes 
on A. Now an object is seen in the direction 
which the visual ray has at the instant of arriving 
at the eye, without regard to what may have been 
otherwise its course between the object and the 
eye. Hence the star S will not be seen in the 
direction A S, but in that of A 5, a tangent to the 
curve S D C B A, at A. Eut because the curve 
described by the refracted ray is concave down- 
wards, the tangent A s will lie above A S, the 
unrefracted ray; consequently the object S wdll 
appear more elevated above the horizon A H when 
seen through the refracting atmosphere than it 
would appear were there no such atmosphere. 
Since, however, the disposition of the strata is the 
same in all directions around A, the visual ray will 
not be made to deviate laterally, but will remain 



constantly in the same vertical plane SAC, pass- 
ing through the eye, the object, and the earth's 
centre. 

The effect of the air's refraction, then, is to raise 
all the heavenly bodies higher above the horizon 
in appearance than they are in reality. Any such 
body, situated actually in the true horizon, will 
appear above it, or will have some certain apparent 
altitude, as it is called. Even some of those 
actually below the horizon, and which would 
therefore be invisible but for the effect of refrac- 
tion, are, by that effect, raised above it. 

The atmosphere refracts the sun's rays so as to 
bring him in sight every clear day before he really 
rises above the horizon, and to keep him in view 
for some minutes after he is really below it. At 
some times of the year, we see the sun ten minutes 
longer above the horizon than he would be if there 
were no refractions, and about six minutes every 
day at a mean rate. 

To illustrate this, let I E K be a part of the 
earth's surface, covered with the atmosphere 




HGFC, and let HEO be the sensible horizon 
of an observer at E. When the sun is at A, really 
below the horizon, a ray of light A C proceeding 
from him comes straight to C, where it falls on the 
surface of the atmosphere, and there, entering a 
denser medium, it is turned out of its rectilineal 
course A C (/ G and bent down to the observer's 
eye at E, who then sees the sun in the direction 
of the refracted ray e^ZE, which lies above the 
horizon, and, being extended out to the heavens, 
shows the sun at B. 

The higher the sun rises the less his rays are 
refracted, because they fall less obliquely on the 



surface of the atmosphere. Thus, when the sun is 
in the direction of the line E/L continued, he is 
so nearly perpendicular to the surface of the earth 
at E that his rays are but very little bent from a 
rectilineal course. 

The exact estimation of the amount of atmo- 
spheric refraction, or the strict determination of 
the angle S A 5, by which a celestial object at any 
assigned altitude, HAS, (last figure but one,) is 
raised in appearance above its true place, is a very 
difficult subject of physical inquiry, and one on 
which geometers are not yet entirely agreed. The 
difficulty arises from this, that the density of any 



WONDERS OF THE HEAVENS 



291 



stratum of air (on which its refracting power de- 
pends) is affected not merely by the superincumbent 
pressure, but also by its temperature or degree of 
heat. Now, although we know, that, as we recede 
from the earth's surface, the temperature of the air 
is constantly diminishing, yet the law or amount 
of this diminution at different heights is not yet 
fully ascertained. Moreover the refracting power 
of air is perceptibly affected by its moisture ; and 
this, too, is not the same in every part of an aerial 
column. Neither are we acquainted with the laws 
of its distribution. The consequence of our igno- 
rance on these points is to introduce a correspond- 
ing degree of uncertainty into the determination of 
the amount of refraction which affects, to a certain 
appreciable extent, our knowledge of several of the 
most important data of astronomy. The uncer- 
tainty thus induced, however, is confined within 
such extremely narrow limits as to be no cause 
of embarrassment, except in the most delicate 
inquiries. 

A "Table of Refractions," as it is called, or a 
statement of the amount of apparent displacement 
arising from this cause at all altitudes, or in every 
situation of a heavenly body from the horizon to 
the zenith, and under all the circumstances in 
which astronomical observations are usually per- 
formed that may influence the result, is one of 
the most important and indispensable of all astro- 
nomical tables, since it is only by the use of such a 
table we are enabled to get rid of an illusion which 
must otherwise pervert all our notions respecting 
the celestial motions. 

In the zenith, there is no refraction. A celestial 
object situated vertically overhead is seen in its 
true direction, as if there were no atmosphere. 

In descending from the zenith to the horizon, the 
refraction continually increases, objects near the 
horizon appearing more elevated by it above their 
true directions than those at a high altitude. 

The rate of its increase is nearly in proportion to 
the tangent of the apparent angular distance of the 
object from the zenith. But this rule, which is not 
far from the truth at moderate zenith distances, 
ceases to give correct results in the vicinity of the 



horizon, where the law becomes much more com- 
plicated in its expression. 

The average amount of refraction for an object 
half-way between the zenith and horizon, or at an 
apparent altitude of forty-five degrees, is about 
one minute, a quantity hardly sensible to the 
naked eye; but at the visible horizon, it amounts 
to no less a quantity than thirty-three minutes, 
which is rather more than the greatest apparent 
diameter of either the sun or the moon. Hence it 
follows, that, when we see the lower edge of the 
sun or moon just apparently resting on the horizon, 
its whole disk is in reality below it, and would be 
entirely out of sight, and concealed by the con- 
vexity of the earth, but for the bending round it 
which the rays of light have undergone in their 
passage through the air. 

It follows from this that one obvious effect of 
refraction must be to shorten the duration of night 
and darkness by actually prolonging the stay of 
the sun and moon above the horizon. But even 
after they are set, the influence of the atmosphere 
still continues to send us a portion of their light; 
not, indeed, by direct transmission, but by reflection 
upon the vapors and minute solid particles which 
float in it, and perhaps, also, on the actual material 
atoms of the air itself. To understand how this 
takes place, we must recollect that it is not only 
by the direct light of a luminous object that we 
see, but that whatever portion of its light is inter- 
cepted in its course and thrown back or laterally 
upon us, though it could not otherwise reach our 
eyes, becomes to us a means of illumination. Such 
reflective obstacles always exist floating in the 
air. The whole course of a sunbeam penetrating 
through the chink of a window-shutter into a dark 
room is visible as a bright line in the air ; and even 
if it be stifled, or let out through an opposite 
crevice, the light scattered through the apartment 
from this source is sufficient to prevent entire 
darkness in the room. The luminous lines occa- 
sionally seen in the air in a sky full of partially- 
broken clouds, which many term "the sun drawing 
water," are similarly caused. They are sunbeams 
through apertures in clouds, partially intercepted 



292 



WONDERS OF THE HEAVENS 



and reflected by the dust and vapors of the air 
below. Thus it is with those solar rays which, 
after the sun is itself concealed by the convexity 
of the earth, continue to traverse the higher 
regions of the atmosphere above our heads, and 
pass through and out of it without directly striking 
on the earth at all. Some portion of them is 
intercepted and reflected by the floating particles 
above mentioned, and thrown back or laterally 
so as to reach us and afford us that secondary 
illumination which is twilight. The course of such 
rays will be immediately understood from the 
annexed figure, in which A B C D is the earth, A 




a point on its surface where the sun S is in the act 
of setting, its last lower ray SAM just grazing 
the surface at A, while its superior rays SN, SO 
traverse the atmosphere above A without striking 
the earth, leaving it finally at the points PQR, 
after being more or less bent in passing through it, 
the lower most, the higher less, and that which 
(like S R 0) merely grazes the exterior limit of the 
atmosphere not at all. Let us consider several 
points, A, B, C, D, each more remote than the 
last from A, and each more deeply involved in the 
earth's shadow, which occupies the whole space 
from A beneath the line A M. Now, A just re- 
ceives the sun's last direct ray, and, besides, is 
illuminated by the whole reflective atmosphere 
P Q, R T. It therefore receives twilight from the 
whole sky. The point B, to which the sun has 
set, receives no direct solar light, nor any, direct 
or reflected, from all that part of its visible atmo- 
sphere which is below ARM; but from the portion 
P R a:, which is traversed by the sun's rays, and 
which lies above the visible horizon B R of B, it 



receives a twilight, which is strongest at R, the 
point immediately below which the sun is, and 
fades away gradually towards P, as the luminous 
part of the atmosphere thins off. At C, only the 
last or thinnest portion P Q, ^r of the lenticular 
segment thus illuminated lies above the horizon 
C Q, of that place. Here, then, the twilight is 
feeble, and confined to a small space in and near 
the horizon which the sun has quitted, while at D 
the twilight has ceased altogether. 

From the explanation we have given of the 
nature of atmospheric refraction, and the mode in 
which it is produced in the progress of a ray of 
light through successive strata or layers of the 
atmosphere, it will be evident, that, whenever a ray 
passes oUiquely from a higher level to a lower one, 
or vice versa, its course is not rectilinear, but 
concave downwards. Of course, any object seen 
by means of such a ray must appear deviated from 
its true place, whether that object be, like the 
celestial bodies, entirely beyond the atmosphere, 
or like the summits of mountains seen from the 
plains, or other terrestrial stations seen from 
each other at different levels, immersed in it. 
Every difference of level, accompanied as it must 
be with a difference of density in the aerial strata, 
must also have corresponding to it a certain amount 
of refraction — less, indeed, than what w^ould be 
produced by the whole atmosphere, but still often 
of very appreciable and even considerable amount. 
This refraction between terrestrial stations is 
termed terrestrial refraction to distinguish it from 
that total effect which is only produced on celestial 
objects, or such as are beyond the atmosphere, 
and which is called celestial or astronomical 
refraction. 

Another effect of refraction is to distort the 
visible forms and proportions of objects seen near 
the horizon. The sun, for instance, which, at a 
considerable altitude, always appears round, as- 
sumes a flattened or oval outline as it approaches 
the horizon, its horizontal diameter being visibly 
greater than that in a vertical direction. When 
very near the horizon, this flattening is evidently 
more considerable on the lower side than on the 



^«jmjll..JiJi.J<.>l»l»J...l...,;.^x.^rj^l^..^.^„^,_». 



WONDERS OF THE HEAVENS 



293 



upper, so that the apparent form is neither circular 
nor elliptic, but a species of oval, which deviates 
more from a circle below than above. This 
singular effect, which any one may notice in a fine 
sunset, arises from the rapid rate at which the 
refraction increases in approaching the horizon. 
Were every visible point in the sun's circumference 
equally raised by refraction, it would still appear 
circular, though displaced ; but the lower portions 
being more raised than the upper, the vertical 
diameter is thereby shortened, while the two 
extremities of its horizontal diameter are equally 
raised and in parallel directions, so that its appa- 
rent length remains the same. The dilated size 
(generally) of the sun or moon when seen near the 
horizon beyond what they appear to have when 
high up in the sky, has nothing to do with refrac- 
tion. It is an illusion of the judgment arising from 
the terrestrial objects interposed or placed in 
close comparison with them. In that situation, we 
view and judge of them as we do of terrestrial 
objects — in detail, and with an acquired habit of 
attention to parts. Aloft, we have no associations 
to guide us, and their insulation in the expanse of 
sky leads us rather to undervalue than to overrate 
their apparent magnitudes. Actual measurement 
with a proper instrument corrects our error, with- 
out, however, dispelling our illusion. By this, we 
learn that the sun, when just on the horizon, 
subtends at our eyes almost exactly the same 
angle, and the moon one materially less, than 
when seen at a great altitude. 

Aberration. But it is not from refraction only 
that a difficulty arises in finding the true places of 
celestial bodies. They are subject to one irregu- 
larity, among others, arising from the motion of 
light. This is a discovery of Dr. Bradley, and as 
the subject is exceedingly curious and important, 
we shall present the reader with an account of it 
nearly in his own words. 

Bradley, in concert with another gentleman, in 
the year 1725, formed a project for verifying, by a 
series of new observations, those which Hooke had 
previously communicated to the public respecting 
the annual parallax of the fixed stars. The instru- 



ments were completed and ready for taking obser- 
vations about the end of November; and on the 
3d of December, a bright star, named Gamma in 
the head of the Dragon, was observed as it passed 
near the zenith, and its situation carefully taken 
with the instrument. The like observations were 
made on the fifth, eleventh, and twelfth of the same 
month, and no material difference of the star was 
observable. An observation, however, was taken 
on the seventeenth by Bradley, who perceived that 
the star now passed a little more southerly than 
when it was before observed. He at first concluded 
that this appearance was owing to the uncertainty 
of his observations; but repeating his observation 
on the twentieth, he found that the star passed still 
more southerly. 

This sensible alteration was the more surprising 
because it was in a direction contrary to what it 
would have been had it proceeded from an annual 
parallax of the star. Well satisfied that it could 
not be entirely owing to a want of exactness in the 
observations, he began to think that some altera- 
tion in the materials of the instrument itself might 
have occasioned it. At length, by repeated trials, 
being fully convinced of the great accuracy of the 
instrument, and finding that there must be some 
regular cause t,o produce so regular an effect, he 
took care to examine nicely, at the time of each 
observation, how much the change of place amounted 
to, and about the beginning of March, 1726, the 
star was found to be twenty seconds farther south 
than at the first observation. It seemed now to 
have arrived at its utmost limit south, for, in 
several observations about this time, no variation 
could be detected in its situation. In the middle 
of April, it appeared to be returning toward the 
north, and about the beginning of June, it passed 
about the same distance from the zenith as it had 
done in the previous December. It continued to 
move northward till September, when it again 
became stationary, being nearly twenty seconds 
more northerly than it had been in March. From 
September, it returned south till it arrived, in 
December, at the same situation which it occupied 
a twelvemonth previous, allowing for the difference 



294 



WONDERS OF THE HEAVENS. 



of declination caused by the precession of the 
equinoxes. 

A nutation of the earth's axis was one of the things 
that occurred to his mind as a cause of this motion 
of the star; but, on consideration, it was found 
insufficient, for though the change of declination in 
the star Gamma of the Dragon might have been 
accounted for by it, it would not at the same time 
agree with the phenomena of the other stars, 
particularly with a small one nearly opposite in 
right ascension, and at about the same distance 
from the north pole of the equator, as it appeared, 
upon a comparison of the observations made upon 
the same days, at different seasons of the year, 
that the latter star changed its declination only 
about half as much as the former, when if nutation 
had been the cause, both stars would have experi- 
enced nearly equal alterations. Upon a farther 
comparison of the observations with each other, it 
was discovered, that, in both the stars before 
mentioried, the apparent difference of declination 
from the maxima was always nearly proportional 
to the versed sine of the sun's distance from the 
equinoctial points. Still no hypothesis was framed 
at that time sufficient to account for all the phe- 
nomena. Bradley erected another instrument, more 
suitable for the purpose of learning in what manner 
other stars were affected by the same cause. 

His instrument being fixed, he immediately 
began to observe such stars as he thought most 
likely to give him an insight into the cause of the 
motion he had already witnessed in two. As 
there were no less than twelve that he observed, 
it was not long before he perceived that the 
notion he before entertained of the stars being 
farthest north and south when the sun was near 
the equinoxes was true of those only that were 
near the solstitial colure. After a time, he dis- 
covered, what he then supposed to be a general 
law, namely, that each of the stars became station- 
ary, or was farthest north or south, when it passed 
over his zenith at six o'clock, either in the morning 
or evening. He perceived, also, that whatever 
situation the stars had with respect to the cardinal 
points of the ecliptic, the apparent motion of all 



tended the same way when they passed his instru- 
ment about the same hour : they moved southward 
when they passed in the day, and northward when 
they passed in the night, so that each was farthest 
north when it came about six o'clock in the evening, 
and farthest south when it came about six in the 
morning. 

When the year was completed, Bradley began to 
examine and compare his observations ; and having 
pretty well satisfied himself as to the general laws 
of the phenomena, he then endeavored to discover 
their cause. With singular sagacity, he conjectured 
that all the phenomena might proceed from the 
progressive motion of light and the earth's annual 
revolution in its orbit. He perceived, that, if the 
motion of light be progressive, the apparent place 
of a fixed object would not be the same when the 
eye is at rest as when it is moving in any other 
direction than that of the line passing through the 
eye and the object, and that, M'hen the eye is 
moving in different directions, the apparent place 
of the object would be different. 

That the aberration of the stars is occasioned by 
the motion of light may be shown by a figure. Let 



"{ ^lf\ \ ^ 




A B represent a part of the earth's orbit, and C B 
a ray of light falling from a star perpendicularly 
upon the line B A. If the eye be at rest at B, the 
object will appear in the direction BC, whether 
light be propagated in time or instantaneously ; but 
if the eye be moving from A toward B, and light 
be propagated with a velocity that is to the velocity 
of the eye as C B is to A B, that particle of it by 



WONDERS OF THE HEAVENS 



295 



which the object will be discerned when the eye 
comes to B will be at C when the eye is at A. 
The star, therefore, will appear in the direction 
AC, and, as the earth moves through equal parts 
of its orbit A a, ab, be, &c., the light coming from 
the star will move through the equal divisions 
ci, ik, kl, &c., and the star will appear succes- 
sively in the directions ce, bf, eg, &c., which are 
parallel to A C, so that, when the eye comes to B, 
the object will be seen in the direction B D. 

The difference between the true and apparent 
places will be greater or less according to the 
proportion between the velocity of light and that 
of the eye. If the velocity of light be to the velocity 
of the earth's motion in its orbit as one thousand 
to one, it may be proved by trigonometry that the 
apparent place of the object from Avhich the light 
proceeds will constantly differ from its true place 
about three minutes and a half, so that a star at 
the pole of the ecliptic would seem to describe 
round that pole a circle whose diameter would be 
seven minutes. 

From a number of observations made by Bradley 
upon the same stars for three years, he found that 
their apparent differed from their true places by 
about twenty seconds, by which means it is proved 
that the velocity of light is about eight thousand 
seven hundred and ninety-four times greater than 
the velocity of the earth in its orbit. But the 
velocity of the earth is about sixty-eight thousand 
miles an hour, and therefore light will pass from 
the sun to the earth in a little more than eight 
minutes, and as this is nearly the same with that 
found by Roemer, (stated in another part of this 
treatise,) and was deduced from a different phe- 
nomenon, the progressive motion of light is placed 
beyond a doubt. It appears, from various observa- 
tions, that the direct light of the sun and stars, as 
well as the reflected light of the planets and their 
satellites, traverses the spaces between them and 
us with the same uniform velocity, and that the 
light of the fixed stars proceeds with the same 
velocity, from whatever distance it comes. 

The aberration of light is a direct proof of the 
motion of the earth in its orbit, and a new confirma- 



tion of the truth of the Copernican theory. And 
with those minds that require immediate and 
sensible proof of the earth's motion, that judge not 
from calculations but from facts, the observations 
of Bradley ought to have great weight. He has 
discovered that the motion of light, combined with 
that of the earth, produces an apparent difference 
in the places of the fixed stars ; and as this motion 
is found to affect all the stars according to their 
situations, such a similarity of variations is sufficient 
to justify the truth of the cause on which they are 
supposed to depend, and to show that the Coper- 
nican theory of the world is conformable to nature 
and the order of things. 

Precession of the Equinoxes and Nutation. 
The equinoxes, or equinoctial points, are those 
points where the ecliptic or apparent annual path 
of the sun crosses the equator. The same course of 
observations by which the path of the sun is traced 
among the fixed stars, determines the place of the 
equinox at that time. This is a point of great im- 
portance, as it is the zero point of right ascension. 
Now when this process is repeated at distant 
intervals of time, a very remarkable phenomenon is 
observed, viz. that the equinox does not preserve a 
constant place among the stars, but shifts its posi- 
tion, travelling continually and regularly, although 
with extreme slowness, backward along the 
ecliptic from east to west, or the contrary to that 
in which the sun appears to move in the same 
circle. The equinoctial point thus moving, as it 
were, to meet the sun in its apparent annual round, 
the earth arrives at the equinoctial point sooner, 
that is, the time of the equinox happens sooner, 
than it would otherwise do ; hence the recession of 
the equinoctial point causes a precession in the time 
of the equinox. The amount of the motion by 
which the equinox travels backward on the ecliptic 
is fifty and one tenth seconds annually, — a minute 
quantity, but which, by its continual accumulation, 
at last makes itself very palpable, and that in a way 
very inconvenient to practical astronomers, by 
destroying in the lapse of a number of years the 
arrangement of their catalogues of stars, and 
making it necessary to reconstruct them. Since 



296 



WONDERS OF THE HEAVENS. 



I 



the formation of the earliest catalogue on record, 
the place of the equinox has retrograded about 
thirty degrees. The period in which it performs a 
complete tour of the ecliptic is 25,868 years. 

The immediate effect of the precession of the 
equinoxes is to produce a uniform increase of longi- 
tude in all the heavenly bodies, whether fixed or 
erratic. For the vernal equinox being the initial 
point of longitudes as well as of right ascension, a 
retreat of this point on the ecliptic tells upon the 
longitudes of all alike, whether at rest or in motion, 
and produces, so far as its amount extends, the 
appearance of a motion in longitude common to all, 
as if the whole heavens had a slow rotation round 
the poles of the ecliptic in the long period above 
mentioned, similar to what they have in twenty- 
four hours round those of the equinoctial. 

To form a just idea of this curious astronomical 
phenomenon, however, we must abandon, for a 
time, the consideration of the ecliptic, as tending 
to produce confusion in our ideas, for this reason, 
that the stability of the ecliptic itself among the 
stars is only approximate, and that, in consequence, 
its intersection with the equinoctial is liable to a 
certain amount of change, arising from its fluctua- 
tion, which mixes itself with what is due to the 
principal cause of the phenomenon. This cause 
will become at once apparent, if, instead of regard- 
ing the equinox, we fix our attention on the pole of 
the equinoctial, or the vanishing point of the 
earth's axis. 

The place of this point among the stars is easily 
determined, at any epoch, by the most direct of all 
astronomical observations. By an astronomical 
instrument, we are enabled to ascertain, at every 
moment, the exact distance of the polar point from 
any three or more stars, and therefore to lay it 
down, by triangulating from these stars, with 
unerring precision, on a chart or globe, without 
the least reference to the position of the ecliptic, or 
to any other circle not naturally connected with it. 
Now, when this is done with proper diligence and 
exactness, it results, that, although for short 
intervals of time, such as a few days, the place of 
the pole may be regarded as not sensibly variable, 



yet in reality it is in a state of constant, although 
extremely slow motion; and, what is still more 
remarkable, this motion is not uniform, but com- 
pounded of one principal, uniform, or nearly 
uniform, part, and other smaller and subordinate 
periodical fluctuations, the former giving rise to the 
phenomena of precession, the latter to another dis- 
tinct phenomenon called nutation. These two phe- 
nomena, it is true, belong, theoretically speaking, 
to one and the same general head, and are intimately 
connected together, forming part of a great and 
complicated chain of consequences flowing from 
the earth's rotation on its axis ; but it will 
conduce to present clearness to consider them 
separately. 

It is found, then, that, in virtue of the uniform 
part of the motion of the pole, it describes a circle 
in the heavens around the pole of the ecliptic as a 
centre, keeping constantly at the same distance of 
twenty-three degrees and twenty-eight minutes 
from it, in a direction from east to west, and with 
such a velocity that the annual angle described by 
it in this its imaginary orbit is 50'M0, so that 
the whole circle would be described by it in the 
above-mentioned period of 25,868 years. It is 
easy to perceive how such a motion of the pole will 
give rise to the retrograde motion of the equinoxes ; 
for in the figure, suppose the pole P, in the progress 




of its motion in the small circle P Z round K, to 
come to 0, then, as the situation of the equinoctial 
E V Q is determined by that of the pole, this, it is 
evident, must cause a displacement of the equinoc- 
tial, which will take a new situation, E U Q,, ninety 
degrees distant in every part from the new position 
of the pole. The point U, therefore, in which 



WONDERS OF THE HEAVENS 



297 



the displaced equinoctial will intersect the ecliptic, 
i. e. the displaced equinox, will lie on that side of 
V, its original position, towards which the motion 
of the pole is directed, or to the westward. 

The precession of the equinoxes thus conceived, 
consists, then, in a real but very slow motion of the 
pole of the heavens among the stars, in a small 
circle round the pole of the ecliptic. Now this 
cannot happen without producing corresponding 
changes in the apparent diurnal motion of the 
sphere, and the aspect which the heavens must 
present at very remote periods of" history. The 
pole is nothing more than the vanishing point of the 
earth's axis. As this point, then, has such a motion 
as described, it necessarily follows that the earth's 
axis must have a conical motion, in virtue of which 
it points successively to every part of the small 
circle in question. We may form the best idea of 
such a motion by noticing a child's peg-top when 
it spins not upright, or that amusing toy the te-to- 
tum, which, when delicately executed and nicely 
balanced, becomes an elegant philosophical instru- 
ment, and exhibits, in the most beautiful manner, 
the whole phenomenon in a way calculated to give 
at once a clear conception of it as a fact, and a 
considerable insight into its physical cause as a 
dynamical effect. The reader will take care not to 
confound the variation of the position of the earth's 
axis in space with a mere shifting of the imaginary 
line about which it revolves in its interior. The 
whole earth participates in the motion, and goes 
along with the axis as if it were really a bar of iron 
driven through it. That such is the case is proved 
by the two great facts: 1st, that the latitudes of 
places on the earth, or their geographical situation 
with respect to the poles, have undergone no per- 
ceptible change from the earliest ages. 2dly, that 
the sea maintains its level, which could not be the 
case if the motion of the axis were not accompanied 
with a motion of the whole mass of the earth. 

The visible eifect of precession on the aspect of 
the heavens consists in the apparent approach of 
some stars and constellations to the pole and recess 
of others. The bright star of the Lesser Bear, 

which we call the pole-star, has not always been, 

3S 



nor will always continue to be, our cynosure. At 
the time of the formation of the earliest catalogues, 
it was twelve degrees from the pole. It is now only 
one degree and twenty-four minutes, and will 
approach yet nearer, to within half a degree, after 
which it will again recede, and slowly give place 
to others, which will succeed it in its companionship 
to the pole. After a lapse of about twelve thousand 
years, the star Alpha Lyrae, the brightest in the 
northern hemisphere, will occupy the remarkable 
situation of a pole-star, approaching within about 
five degrees of the pole. 

The nutation of the earth's axis is a small and 
slow subordinate gyratory movement, by which, if 
subsisting alone, the pole would describe among 
the stars, in a period of about nineteen years, a 
minute ellipsis, having its longer axis equal to 
18". 5, and its shorter to 13"". 74, the longer being 
directed towards the pole of the ecliptic, and the 
shorter, of course, at right angles to it. The con- 
sequence of this real motion of the pole is an 
apparent approach and recess of all the stars in the 
heavens to the pole in the same period. Since, 
also, the place of the equinox on the ecliptic is 
determined by the place of the pole in the heavens, 
the same cause will give rise to a small alternate 
advance and recess of the equinoctial points, by 
which, in the same period, both the longitudes and 
the right ascensions of the stars will be also 
alternately increased and diminished. 

Both these motions, however, although here 
considered separately, subsist jointly ; and since 
the pole, while it is describing its little ellipse of 
18". 5 in diameter in virtue of the nutation, is 
carried by the greater and regularly-progressive 
motion of precession over so much of its circle round 
the pole of the ecliptic as corresponds to nineteen 
years, (that is to say, over an angle of nineteen 
times 50'M round the centre, which, in a small 
circle of twenty-three degrees and twenty-eight 
minutes in diameter, corresponds to six minutes 
and twenty seconds as seen from the centre of the 
sphere,) the path which it will pursue in virtue of 
the two motions subsisting jointly will be neither 
an ellipse nor an exact circle, but a gently-undulated 



298 



WONDERS OF THE HEAVENS. 



ring, like that in the next figure, where, however, 
the undulations are much exaggerated. 

These movements of precession and nutation 
are common to all the celestial bodies, both fixed 
and erratic, and this circumstance makes it impos- 
sible to attribute them to any other cause than a 
real motion of the earth's axis, such as we have 
described. Did they only affect the stars, they 
might, with equal plausibility, be urged to arise 
from a real rotation of the starry heavens, as a 
solid shell, round an axis passing through the poles 
of the ecliptic in 25,868 years, and a real elliptic 
gyration of that axis in nineteen years ; but since 
they also affect the sun, moon, and planets, which, 
having motions independent of the general body of 
the stars, cannot without extravagance be supposed 
attached to the celestial concave,* this idea falls 
to the ground, and there only remains, then, a 
real motion in the earth by which they can be 
accounted for. 

Precession and nutation, considered as affecting 
the apparent places of the stars, are of the utmost 
importance in practical astronomy. When we 
speak of the right ascension and declination of a 
celestial object, it becomes necessary to state what 
epoch we intend, and whether we mean the mean 
right ascension, (cleared, that is, of the periodical 
fluctuation in its amount which arises from nuta- 
tion,) or the apparent right ascension, which, being 
reckoned from the actual place of the vernal 
equinox, is affected by the periodical advance and 
recess of the equinoctial points thence produced — 
and so of the other elements. It is the practice of 
astronomers to reduce, as it is termed, all their 
observations, both of right ascension and declina- 
tion, to some common and convenient epoch, such 
as the beginning of the year for temporary purposes, 
or of the decade or the century for more permanent 
uses, Ijy subtracting from them the whole effect of 
precession in the interval, and, moreover, to divest 
them of the influence of nutation by investigating 

* This argument, cogent as it is, acquires additional and decisive 
force from the law of nutation, which is dependent on the position, 
for the time, of the lunar orlit. If we attribute it to a real motion of 
the celestial sphere, we must then maintain that sphere to be kept in 
a constant state of tremor by the motion of the moon. 



and subtracting the amount of change, both in right 
ascension and declination, due to the displacement 
of the pole from the centre to the circumference 
of the little ellipse above mentioned. This last 
process is technically termed correcting or equating 
the observation for nutation, by which latter word 
is always understood, in astronomy, the getting I'id 
of a periodical cause of fluctuation, and presenting 
a result, not as it was observed, but as it would 
have been observed had that cause of fluctuation 
had no existence. 

For these purposes, in the present case, very 
convenient formulae have been derived, and tables 
constructed ; but they are of too technical a 
character for this work. We shall, however, point 
out the manner in which the investigation is con- 
ducted. Suppose the triangle K P X projected on 
the plane of the ecliptic as in the annexed figure. 




In the triangle K P X, K P is the obliquity of the 
ecliptic, K X the co-latitude, or complement of lati- 
tude, and the angle PKX the co-longitude of the 
object X. These are the data of our question, of 
which the first is constant, and the two latter are 
varied by the effect of precession and nutation ; and 
their variations (considering the minuteness of the 
latter effect generally, and the small number of 
years, in comparison to the whole period of 25,868, 
for which we ever require to estimate the effect of 
the former) are of that order which may be 
regarded as infinitesimal in geometry, and treated 
as such without fear of error. The whole question, 
then, is reduced to this: — In a spherical triangle 
K P X, in which one side K X is constant, and an 
angle K and adjacent side K P vary by given 
infinitesimal changes of the position of P, required 



WONDERS OF THE HEAVENS 



299 



the changes thence arising in the other side P X, 
and the angle K P X. This is a problem of 
spherical geometry, and being resolved, it gives at 
once the reductions we are seeking ; for P X being 
the polar distance of the object, and the angle 
K P X its right ascension plus ninety degrees, their 
variations are the very quantities we seek. It only 
remains, then, to express in proper form the amount 
of the precession and nutation in longitude and 
latitude, when their amount in right ascension and 
declination will immediately be obtained. 

The precession in latitude is zero, since the 
latitudes of objects are not changed by it : that in 
longitude is a quantity proportional to the time, at 
the rate of 50'M0 per annum. With regard to the 
nutation in longitude and latitude, these are no other 
than the abscissa and ordinate of the little ellipse 
in which the pole moves. 

Obliquity of the Ecliptic. The obliquity of 
the earth's orbit to the equator was long considered 
as a constant quantity. True, its values as assigned 
by astronomers in different ages do not agree with 
each other. They have been continually diminishing 
from the time of the earliest astronomers until now. 
Yet, as late as the end of the seventeenth century, 
this variation in the observations was generally 
attributed to their inaccuracy, and to a want of 
knowledge of the parallaxes and refraction of the 
heavenly bodies. These variations cannot be 
ascribed wholly to the imperfections of instruments 
and observations ; for, had this been the case, the 
results obtained must have been sometimes too 
great as well as too small. There is no reason to 
suppose that all could have agreed in indicating a 
progressive diminution of the obliquity of the 
ecliptic, if this diminution were not real. Accord- 
ingly, it appears from the most accurate modern 
observations, made at great intervals, that this 
obliquity is diminishing ; and the theory of universal 
gravitation fortunately supplies us with a satisfactory 
explanation of the phenomenon. 

While the earth is revolving in the plane of the 
ecliptic, it is acted upon by all the planets of the 
solar system. The action of the planets, when 
situated in the plane of the ecliptic, have a tendency 



not only to alter the earth's gravity to the sun, or 
to accelerate and retard its motion ; but as all the 
planets move in orbits inclined to the ecliptic, their 
action tends to bring the earth towards the plane 
of their orbits. The effect of this action, then, is to 
displace the ecliptic, or diminish the inclination of 
the earth's orbit to the plane of the orbit of the 
planet ; but while the earth's orbit is thus changing 
its position, the equator of the earth is undergoing 
no change ; consequently there will result a varia- 
tion in the inclination of the ecliptic to the equator. 
This change, however, is very small, and scarcely 
becomes apparent till after the lapse of many years. 
According to the present disposition of the system, 
the inclination of the ecliptic to the equator must 
diminish about fifty-two minutes in a century, or 
about half a second in a year. In the following 
table, are contained observations, made at times 
widely distant, of the angle formed by the ecliptic 
with the equator. 



Time of the observa- 
tions. 

B. C. 1100 

350 

50 



Observed obliquity. 

23° 54' 02" 
23° 49' 20" 
23° 45' 39" 



Time of the observa- 
tions. 

A. C. 1279 
1437 
1756 



Observed obliquity. 

23° 32' 02" 
23° 31' 48" 
23° 28' 13" 



On the 1st of January, 1837, the inclination was 
23° 27' 37".89. The observations in the above 
table, taken together, put beyond all doubt the pro- 
gressive diminution of the angle in question, and, 
from a comparison of their results with those ot 
theory, it is rendered certain that the diminution 
is owing solely to the cause indicated by theory, 
viz. to the attraction of the sun upon the planets, 
and of the different planets upon each other. 

The effect of this diminution is also perceived 
when the positions of the same stars with respect 
to the ecliptic at distant periods are compared. 
The effect is most remarkable in the stars situated 
near the summer and winter solstices.* Those 
which were formerly situated north of the ecliptic, 
near the summer solstice, are now found to be still 
farther north, and farther from this plane. On the 
contrary, those which, according to the testimony 
of ancient astronomers, were situated south of the 

* The solstices are the points where the ecliptic touches the 
tropics. 



300 



WONDERS OF THE HEAVENS 



ecliptic, near the same solstice, have approached 
this plane, and some of them are now situated in it, 
or just on the north side of it. Similar changes 
have happened to those stars situated near the 
winter solstice. All the stars participate in this 
motion, but difterently, and the less the nearer 
they are to the line of the equinoxes ; so that this 
line appears to perform the part of a hinge, about 
which the rotation takes place. From these phe- 
nomena, it is natural to conclude that the plane of 
the ecliptic has an actual motion in the heavens, 
and that it thus produces the observed appearances 
of an apparent contrary motion in the stars ; for 
it can scarcely be supposed that these motions 
really belong to the stars, since such a supposition 
would require among all the heavenly bodies a 
corresponding motion, which no one would think of 
maintaining. 

It is important to observe, and theory lends 
confirmation to the truth of the remark, that the 
diminution of the obliquity of the ecliptic will not 
always continue. A period will arrive when this 
motion, growing less and less, will at length en- 
tirely cease, and the angle will for a time appear 
constant, after which the displacement will com- 
mence in the opposite direction. The ecliptic 
will then gradually diverge from the equator by 
the same degrees according to which it before 
approached, and these alternate states will consti- 
tute an endless oscillation, comprehended within 
fixed limits. These limits are not yet discovered ; 
but it can be demonstrated, from the constitution 
of our globe, that such limits exist, and that they 
are very restricted. It may be aflirmed that the 
plane of the ecliptic never has coincided, and 
never will coincide, Avith that of the equator, — a 
circumstance, which, if it could happen, would 
produce on the earth a perpetual spring. 

The method used by astronomers for determining 
the inclination of the ecliptic, to the equator is by 
observing the greatest and least altitudes of the 
sun, one observation being taken at the summer, 
the other at the winter, solstice. Half of the 
difference of the altitudes will be the inclination 
sought. 



SECTION IV. 

The telescope— Its invention— Its simplest form— Mode of finding 
the magnifying power of telescopes— Common astronomical tele- 
scopes—Difficulties encountered in their early construction — 
Huygens' improvement— Newton's lenses— Eeflecting telescopes 
— The Newtonian— The Gregorian — The Cassegrainian— W. Her- 
schel's—Eatnage's— General remarks on telescopes— Impossibility 
of minute discoveries in the moon. 

A telescope is an optical instrument employed 
for viewing distant objects by increasing the appa- 
rent angle under Avhich they are seen without its 
assistance, and hence the effect on the mind of an 
increase in size, or, as commonly termed, magnified 
representation. The construction of the telescope 
is, perhaps, one of the most important acquisitions 
that the sciences ever attained, as it unfolds to our 
view the loonders of the heavens, and enables us to 
obtain data for astronomical and nautical purposes. 

The invention of this instrument is somewhat 
uncertain, and is ascribed to different individuals, 
as John Baptista Porta, Jansen of Middleburg, and 
Galileo. The time of its first construction was 
about the year 1590. 

The simplest construction of this instrument 
consists of two convex lenses, so combined as to 
increase the apparent angle under which distant 
objects are seen. If we place two convex lenses 
with a distance between them equal to the sum of 
their foci, a telescope will be formed, and the 
magnifying power will be in proportion to the focus 
of the two lenses. Let o be the object-lens, and 




suppose it eight inches focus, and e the eye-lens, of 
two inches focus. The distance between these two 
lenses must be ten inches if the object be at an 
infinite distance, as a star ; but when the object is 
terrestrial, the distance between the two lenses 
must be increased to adjust them for distinct vision. 
On this account, the eye-lens is mounted in a tube, 
sliding within another tube in which the object-glass 
is fixed, and, therefore, can be drawn out for near 
objects. As the size of objects is dependent on 



WONDERS OF THE HEAVENS 



301 



the angle under which they are seen, the image F, 
formed by the object-glass, will subtend, in the focus 
of the eye-glass e, the angle c ed, which is four 
times the angle cod that the object subtends, for 
the distance i^o is four times Fe: hence the mag- 
nifying power may be found by dividing the focal 
length of the object-glass by the focus of the eye- 
glass, when the quotient will be the power. 
Objects seen through this telescope are inverted, 
and on that account it is inapplicable to land obser- 
vation; but at sea, it is occasionally used at night, 
and in hazy weather when there is little light, and 
is hence called a night telescope. 

The common astro?iomical telescope is of the same 
principle of construction as the preceding. The 
inversion of the object is immaterial in its applica- 
tion to celestial observations ; but the disadvantage 
of this instrument is felt when very high powers 
are required, for then the objects are rendered 
dark and obscure, and if the aperture of the object- 
glass is increased to admit more light, the formation 
of the object is confused. Huygens, however, made 
a telescope of this construction, in which he was 
enabled to use an aperture of six inches, by making 
the focus of the object-glass one hundred and 
twenty-three feet in length. With this, by chang- 
ing the eye-lenses, any required power was 
produced. 

The field of vision, or number of objects, seen by 
the telescope above described, is very limited, the 
eye-lens not being sufficiently large, as is shown 
by the dotted lines i i in the figure, which do not 
enter the eye-lens e, and are not received by the 
eye. Now, if the diameters of this lens were 
increased, the objects would be rendered indistinct, 
arising from the rays, spread over the surface of 
the lens from any point in the object, not being 
collected again in another point after refraction. 
This error is occasioned by the figure of the lens, 
and is called the spherical aberration by figure. 

The great advantage of duly considering the 
aberration of lenses will be evident if we combine 
two lenses of twice the focal distance, instead of 
one, to produce any given power, as the aberration 
\v\\\ be decreased to one quarter of that of a single 



lens of equivalent power, and, therefore, the aper- 
ture of the compound lens may be increased, while 
the error will be less than in a single lens. In the 
common telescopes, if two lenses were used instead 
of the single object and eye-glass, as shown in the 
above figure, the apertures of each might be 
increased, and consequently the instruments would 
be improved in light and field. 

Huygens has demonstrated, that, when the 
greatest possible distinctness is required for the 
eye-piece of a telescope, it may be obtained by two 
plano-convex lenses, placed, as in the adjoining 
figure, with their plane sides outward, and the focus 




of the eye-lens E must be two thirds of that of the 
field-lens F, with a distance between them equal to 
the difference of their focal lengths. This combina- 
tion, from the purpose it has been adapted to, is 
called the astronomical positive eye-piece ; and the 
telescope, by this addition, will have four times the 
distinctness of a single lens D of equivalent power, 
while the distortion of the object will only be one 
fourth of that produced by a single lens; for the 
refraction of the object-lens brings the image of the 
marginal rays nearer to itself than the central, 
therefore the image will be formed convex next 
the lens F, as shown by the arrow, and as the 
radius of curvature of the lens F is twice that of 
the single lens D, the distortion will be decreased 
in the square of this ratio, or four times. On this 
account, a similar combination is used for the eye- 
pieces of telescopes for astronomical quadrants 
and other graduated instruments when the convex 
side of the field-lens is turned towards the eye- 
glass E, because equal divisions on a micrometer 
correspond with equal angles subtended by objects 
measured with this instrument. This combination, 
which is called Ramsden's Micrometical Eye- 
piece, has one great disadvantage, viz. that it 
requires the eye to be placed exceedingly near to 
the eye-lens E. 



302 



WONDERS OF THE HEAVENS 



Being now in possession of a combination that 
will diminish the aberration produced by the eye- 
piece of a telescope, om' limit of magnifying power 
and light will arise from the errors occasioned by 
the object-glass ; and this may be diminished by 
having the curves of the two surfaces as one to six, 
with the most convex side outermost ; for this lens 
has less aberration than any other. Secondly, by 
using two lenses of twice the focus in contact, to 
produce the required refraction, and thus diminish 
the error four times. But, although this error may, 
by the means here pointed out, be rendered very 
small and almost imperceptible, yet it is magnified 
in the same proportion as the objects ; and when 
high powers are used, the indistinctness will become 
sensible. 

Sir Isaac Newton conceived that the surfaces of 
the lens might be formed of some mathematical 
curve which would entirely obviate this error ; and 
by investigation he found that, if the surface were 
described by the revolution of a parabola, and the 
radiant or object be at an infinite distance, the rays 
would be collected to a point, and be free from all 
aberration. He afterwards formed tools to grind 
and polish lenses of this figure; but, when made, 
although the error by figure was perfectly correct- 
ed, it was discovered that the white heterogeneous 
pencils of light (before that time considered as 
homogeneous) in their passage through the lens 
were divided into their several constituents of red, 
orange, green, blue, and violet, in the same man- 
ner as by a prism, and hence lenses of this figure 
became useless. 

With these disadvantages to contend against in 
refracting substances. Sir Isaac Newton, in the year 
1666, turned his attention to reflected light, in 
which the angle of all the colored rays is equal. 
By pursuing this idea he entirely obviated the 
chromatic error. In the first telescope he made 
by reflection, the distinctness with which objects 
were seen through it was surprising when compar- 
ed with the refracting telescopes of those times; 
for, though the focal distance of the metal was only 
six and one-third inches, it would carry a power of 
thirty-eight with equal distinctness to a four feet 



refractor. The form of the metal was spherically 
concave, but by investigation he ascertained that if 
the form had been that of a parabola, there would 
not have been any spherical aberration produced ; 
and if we examine the spherical aberration by fig- 
ure of a spherically concave metal, and compare it 
with that of a plano-convex lens ground in the 
same tool, the former will be four, while the latter 
is nine. But when it is considered that the focus 
of the glass lens is four times that of the metal, 
(for the focal distance of a plano-convex lens is 
twice the radius, and that of the concave reflector 
half the radius,) to make their foci equal, the curv- 
ature of the lens must be four times that of the 
speculum ; and it has been shown that the error by 
figure increases inversely as the square of the ra- 
dius; hence the aberration of the lens will be to 
that of the reflector as 4^ x 9 to 4, or as 36 to 1, 
and the distinctness will be inversely as the areas of 
these circles, which are as the squares of their re- 
spective diameters; so that the distinctness of a 
reflector will be 1296 times greater than that of a 
lens of the same focus and aperture. 

The Newtonian telescope consists of a concave 
parabolic metal A, fixed at the end of the tube 




d d d; the plane speculum c is fixed to a wire, hav- 
ing its other end attached to a dove-tailed sliding- 
piece i i, and the face of the plane metal is inclined 
to the axis of the tube and the large speculum at 
an angle of forty-five degrees. In the sliding-piece 
i i, opposite the small metal, is inserted a short tube 
to hold an eye-piece, which is a single lens with its 
flat side outermost, or the astronomical eye-piece ; 
but as the color produced by these eye-lenses is 
not corrected, another combination, called the 
negative achromatic eye-piece, should be used. 
The adjustment of this instrument to distinct vision 
is made by a rack and pinion attached to the 
sliding-piece and great tube of the telescope, by 



WONDERS OF THE HEAVENS. 



303 



which the eye-piece and small speculum are brought 
nearer or farther from the large metal. Let rr be 
the rays of light coming from a distant object, and 
falling on the large speculum A, these rays would 
be reflected to the focus e ; but meeting with the 
oblique flat metal c, are reflected to /, where an 
image of the distant object will be formed, and is 
received by the eye-lens g, by which the rays are 
rendered parallel. The power of a Newtonian re- 
flector is proportional to the relative focal distances 
of the concave metal and the eye-lens. For exam- 
ple, let the focal distance ^ e be forty inched, and 
the focus of the eye-lens g half an inch, the power 
will be eighty. It should here be observed, that the 
same instrument which is free from aberration for 
astronomical observation will not be so for terres- 
trial uses ; for the rays in the former case are 
parallel, while they are divergent in the other. 
The curve, therefore, of the large speculum, when 
required for the latter purposes, should be ellipti- 
cal, having the object in one focus, and the focus 
of the eye-lens in the other. 

This telescope, which is more simple than other 
reflectors, may be greatly improved according to the 
method of Brewster, who has proposed (for tele- 
scopes of moderate size, where a front view cannot 
be used) to employ two glass prisms in place of the 
small plane. By the experiments of Kater, it 
appears that one-third of the rays of light is lost 
when reflected by a speculum at a vertical inci- 
dence, and probably not more than sixty-eight 
out of one hundred are reflected at an angle of 
forty-five degrees, as in the Newtonian small 
metal. In addition to this, the imperfection of sur- 
face and figure in metals, which makes the rays 
stray five or six times more than the same imper- 
fection in a refracting surface, as well as the 
difficulty of working metals as perfect as glass, 
induced him to suggest this improvement. Let a b 
be the great speculum, and r a, r b parallel rays 
from a distant object reflected to a focus at F ; the 
cone of rays, however, is intercepted by the achro- 
matic prism c d, and refracted to/, where a distinct 
image is formed in the anterior focus of the eye- 
glass e, by which it is magnified. The double 



prism c d being composed of a prism of crown glass 
c, and another of flint d, united by a cement of 




mean refractive power, the loss of light by trans- 
mission through the two prisms, says Brewster, will 
not exceed six hundred rays out of ten thousand, 
as the light transmitted through a lens of glass, ac- 
cording to Herschel, is nine thousand four hundred 
and eighty-five out of ten thousand incident rays. 
Hence the light lost by the prism is only one-fifth 
of that lost by reflection. 

The Newtonian telescopes made by Hadley had, 
in place of a plane metal, a right-angular prism P 
substituted, having its sides perpendicular to the 
incident and emergent rays. In this, as is accom- 
plished by the two prisms of Brewster, the image 
will be erect, and a less quantity of light lost than 
by a mirror of the common kind. 

Another class of reflecting telescopes was in- 
vented by Gregory, in 1660, but they were not 
made till some years after the Newtonian, from 
the difficulty of forming the metals. The Grego- 
rian reflector is, however, preferred to the New- 
tonian, and is most commonly used, because the 
observer is stationed in a line with the object, 
whereas in the Newtonian he is at right angles 
to it. The annexed figure is a section of the 




Gregorian reflector. B D is a concave metal, 
whose surface should be formed by the revolution 
of the hyperbolic curve : this speculum has a 
small hole in its centre. E is another concave 
elliptical small metal placed in the axis of the 



304 



WONDERS OF THE HEAVENS 



larger one, at a distance from it a little more than the 
sum of their focal distances. H are the eye-lenses, 
sliding in a tube fixed behind the large speculum : 
the adjustment is made by the screw s s, which 
moves the small metal to or from the great specu- 
lum. Let r B and r D be two parallel rays from a 
distant object, these will be reflected to the focus F 
of the large metal, where an image will be formed, 
and the rays, crossing each other, fall upon the small 
speculum E ; and if the focus of this metal had co- 
incided with the focus F, the rays would have been 
reflected parallel, but now they form a direct image 
at I, and this image is viewed by the eye-piece or 
a single lens at H. The magnifying power of this 
instrument may be computed thus : — suppose the 
focus B F of the large speculum is nine inches, and 
the focus of the small metal one and one-half inch: 
then will the angle be increased six times ; but 
this must be multiplied by the ratio of the distances 
I H, the focus of the lens, and the distance I F ; 
and if these are as one to eight, the amplification 
of the object will be 6 X 8 = 48 times. 

The Cassegrainian reflector is constructed in the 
same way as the Gregorian, with the exception of 
a small convex spherical speculum, instead of one 
a little concave ; and as the focus of this metal is 
negative, it is placed at a distance from the larger 
metal equal to the difference of their foci, and only 
one image is formed, viz. that in the focus of the 
eye-glass ; on this account, the distinctness is con- 
siderably greater than in the Gregorian. Mr. 
Ramsden states, that this construction is prefera- 
ble to either of the former reflectors, because the 
aberrations of the two metals have a tendency to 
correct each other ; whereas in the Gregorian, 
both the metals being concave, any error in the 
specula will be doubled. By assuming such propor- 
tions of the foci of the specula as are generally 
employed in these instruments, which are about as 
one to four, he asserts that aberration or indistinct- 
ness occasioned by the figures of the reflectors in 
the Cassegrainian construction is to that in the 
Gregorian as three to five. 

In sidereal observations of nebulae and small stars, 
much light is necessarily required; and by what- 



ever means a loss of light by reflection or refraction 
can be prevented, the adoption of such a construc- 
tion would be advisable. Herschel, from an inves- 
tigation of the loss of light occasioned by the small 
spectrum in reflectors, was enabled to construct an 
instrument that entirely obviated the use of the 
second metal. We shall here lay before our 
readers a description of this magnificent instrument, 
Avhich may justly be ranked among the wonders 
of the world. 

But it will not be amiss to mention first a few 
circumstances that led the way to the construction 
of this large telescope, in the execution of which 
two very material requisites were necessary ; viz. 
the support of a very considerable expense, and a 
competent experience and practice in mechanical 
and optical operations. Herschel states that when 
he went to reside at Bath (England) he had long 
been acquainted with the theory of optics and 
mechanics, and only wanted experience in the 
practical part of these sciences. This he acquired 
by degrees at that place, where, in leisure hours, 
and by way of amusement, he made a great num- 
ber of telescopes of different sizes and construc- 
tions. His way of preparing mirrors at that time, 
when the direct method of giving the figure of any 
of the conic sections to specula was still unknown 
to him, was to have many mirrors of each sort 
cast, and to finish them all as well as he could. 
Then he selected for use the best of them by trial, 
putting the rest by to be repolished. In the year 
1781 he began to construct a thirty feet aerial 
reflector, and cast the mirror, which came out of 
the mould thirty-six inches in diameter. The 
composition of the metal being too brittle, it 
cracked in the cooling. He cast it a second time, 
but the furnace gave way and the metal ran into 
the fire. The discovery of the Georgian planet 
soon after introduced him to the patronage of the 
king, to whom the design of constructing a forty 
feet telescope was communicated, and by whom it 
was encouraged. In consequence of the king's 
support, Herschel was enabled to begin the con- 
struction of his immense telescope toward the 
close of the year 1785. He inspected the casting. 



WONDERS OF THE HEAVENS. 



305 



grinding, and polishing of the great mirror, which 
being highly polished and put into the tube, he 
had the tirst view through it on February 19th, 
1787. He did not, however, date the completion 
of the instrument till much later; for the first 
speculum was thinner on the centre of the back 
than was intended, and, on account of its weakness, 
a good figure could not be given to it. A second 
mirror was cast January 26th, 1788, but it cracked 
in cooling. On February 16th it was recast, with 
particular attention to the shape of the back, and it 
proved to be of the proper degree of strength. By 
October 24th it was brought to a good degree of 
polish, and the planet Saturn observed with it. Not 
being satisfied, Herschel continued the work of 
polishing till August 27th, 1789, when it was tried 
upon the fixed stars and found to give a pretty 
sharp image. Large stars were a little affected 
with scattered light, owing to many remaining 
scratches in the mirror. On the 29th of the same 
month, having brought the telescope to the parallel 
of Saturn, Herschel discovered a sixth satellite of 
that planet ; he also saw the spots on Saturn better 
than he had ever seen them before ; so that we may 
date the completion of the forty feet telescope from 
that time. The high magnifying power of Her- 
schel's telescope made all the usual apparatus for 
its support extremely imperfect. But his judgment, 
ingenuity and fertility in resource were as eminent 
as his philosophical ardor. He contrived in this 
case an apparatus that had every desirable property. 
The motions, both vertical and horizontal, Avere 
effected with the utmost simplicity and firmness. 
It was one of the noblest monuments of philosophi- 
cal zeal and princely munificence the world ever 
saw. 

The frontispiece represents a view of this instru- 
ment (in a meridional situation) as it appeared when 
seen from a convenient distance by a person placed 
toward the southwest of it. The foundation in the 
ground consisted of two concentric circular brick 
walls, the outermost of which was forty-two feet in 
diameter, and the inner twenty-one feet. They 
were two feet six inches deep under ground, two 

feet three inches broad at the bottom, and one foot 
39 



two inches at the top, and were capped with paving 
stones about three inches thick and twelve and 
three quarters broad. The bottom frame of the 
whole apparatus rested upon these two walls by 
twenty concentric rollers, and was movable upon a 
pivot, which gave a horizontal motion to the whole 
apparatus as well as to the telescope. In the 
centre was a large post of oak, framed together with 
braces under ground, and walled fast with brickwork 
so as to make it steady. Two central beams cross- 
ed each other over this post, and a strong iron pin 
(the pivot) passed through them both into a socket 
in the centre of the post, thus permitting the whole 
of the foundation timber to turn freely on this 
centre, a proper force being applied for that pur- 
pose. 

The construction of the tube of the telescope 
(though very simple in its form, being cylindrical) 
was attended with great difficulties. This is not to 
be Wondered at, if its size and the materials of 
which it was made are taken into consideration. 
Its length was thirty-nine feet four inches, it mea- 
sured four feet ten inches in diameter, and every 
part of it was of iron. Upon a moderate computa- 
tion, the weight of a wooden tube must have exceed- 
ed the iron one by three thousand pounds at least, 
while its durability would have been far inferior to 
that of iron. The body of the tube was made of 
sheet iron, joined together without rivets, by a 
kind of seaming well known to those who make 
funnels for stoves. The whole outside was thus 
put together, in all its length and breadth, so as to 
make one sheet of near forty feet long and fifteen 
feet four inches broad. The tools, forms, and 
machines necessarily made for the construction 
were very numerous. In the formation of this large 
sheet, a kind of table built for its support was con- 
stantly enlarged as the sheet advanced, till when 
finished it was as large as the whole of it. When 
the whole sheet was formed, the sides were cut per- 
fectly parallel, and bent over at the ends in contrary 
directions to be ready to receive each other. Very 
great mechanical skill was displayed in the con- 
trivance of the apparatus by which the telescope 
was supported and directed. By means of two mo- 



506 



WONDERS OF THE HEAVENS. 



tions, a vertical and a horizontal, the telescope 
might be set to any altitude up to the very zenith ; 
and in order to have the direction of it at command, 
a foot quadrant was fixed at the west side of the 
tube, near its end. Above this was planted a 
finder, or night-glass, about twenty-one inches long, 
with crosswires in the focus. 

The method of observation with this telescope 
was called by Herschel i\iQ front view. The size of 
the instrument having been such as to allow of its 
being loaded with a se^t, there was one fixed to the 
end of it. This seat was movable upward and 
downward through the space of one foot, not so 
much for the accommodation of different observers, 
as for the alteration required at different altitudes, 
which amounted to nearly twelve inches. One half 
of the seat was made to fall down in order to open 
an entrance at the back, and being enclosed at the 
front and sides, a bar, which shut up the back after 
the observer was in his place, secured the whole in 
such a manner as to render it perfectly safe and 
convenient. At the sides of the seat there were 
two strong iron quadrants with teeth, with a handle 
extending to within reach of the observer ; and by 
turning this handle, the seat was brought to a 
horizontal position when any change in the altitude 
of the telescope required it. By making use of 
another handle, the observer could screw himself, 
the seat, and the telescope, back and forth in the 
space between the supporting ladders, and thus 
follow at will the object whose course he wished to 
trace. He might have ordered the whole frame to 
be moved with the great circular motion, and have 
kept his object in view by screwing the telescope 
back as fast as it advanced. Of the two houses re- 
presented in the plate, one contained the assistant's 
room, the other the working-room. A mode of 
ready communication from the observer to the 
assistant, and to the person who gave the required 
motions to the apparatus, was indispensable. But 
the distance between these rooms and the place of 
the observer was evidently too far for a conversa- 
tion in the open air between them. A speaking- 
pipe was therefore constructed to convey the com- 
munications to their proper destination. This pipe 



was divided into two branches, one going into the 
observatory (assistant's room) by passing through 
the floor, the other into the working-room, where 
it ascended to the level of the workman's ear. 
Notwithstanding the passage of the sound through 
a pipe with many inflections and not less than one 
hundred and fifteen feet length, it required no 
particular exertion to be very well understood. In 
the observatory there was a sidereal time-piece; — 
close to it, and of the same height, a polar distance 
piece, with a dial-plate similar and equal in size 
to that of the time-piece. It was divided into sixty 
parts to express minutes of space. The degrees 
were shown in a square opening under the centre. 
This piece might have been set so as to show polar 
distance, zenith distance, declination, or altitude, 
by setting it differently, yet its construction was 
very simple. 

The time and polar distance pieces were so 
placed that the assistant at the table sat facing them, 
with the speaking-pipe rising near, so that observa- 
tions were very readily recorded. The place of 
new objects was also readily noted, as their right 
ascension and polar distance was before the assist- 
ant, so that nothing was required but to read them 
at the signal of the observer. By means of the 
speaking-pipe the workman might have been direct- 
ed to "begin," "stop," "go faster, slower." These 
were generally all the orders necessary for him, 
which fact, being known to him and to the assistant, 
could occasion no mistake, although the pipes that 
went into the two apartments were united. The 
metal of the great mirror was forty-nine and a half 
inches in diameter, but on the rim there was an 
offset three-fourths of an inch broad and one inch 
deep, which reduced the concave face of it to a 
diameter of forty-eight inches of polished surface. 
The thickness, which was the same in every part of 
it, was, after the polishing, about three and a half 
inches. Its weight when it came from the cast was 
two thousand one hundred and eighteen pounds, of 
which it must have lost a small quantity in polish- 
ing. To put the mirror into the tube, a small 
narrow carriage was provided going on rollers. It 
had two upright sides, between which the speculum, 



WONDERS OF THE HEAVENS. 



307 



when suspended vertically by a crane in the labo- 
ratory, was made to pass in at one end, and being 
let down, was bolted in. 

This noble instrument, with proper eye-glasses, 
magnified above six thousand times, and was the 
largest telescope ever constructed. A full account 
of every part of the work which attended the forma- 
tion and erection of this telescope, together with 
minute details of the mode of making observations, 
is contained in the Transactions of the London 



Philosophical Society for 1795. The date of the 
completion of this apparatus was fixed by Herschel, 
as before stated, at the 28th of August, 1789. 

The frame of this instrument having greatly 
decayed, it was taken down, and another, of 
twenty feet focus and eighteen inches diameter, 
erected in its place, by Sir John F. W. Herschel, 
in 1822. 

The largest front-view reflecting telescope at 
present in England, was erected at the Royal Ob- 




servatory, at Greenwich, by Mr. Ramage, in 1820. 
The diameter of the concave reflector is fifteen 
inches, and its focus twenty-five feet ; the mechan- 
ical arrangement of the stand is greatly simpli- 



fied. A perspective view of the whole instrument is 
shown in the above figure. The tube is composed 
of a twelve-sided prism of deal, five-eighths of an 
inch thick ; at the mouth c is a double cylinder of 



308 



WONDERS OF THE HEAVENS. 



different diameters on the same axis; around this 
a cord is wound by a winch, and passes up from 
the small cylinder over a pulley a, and down 
through the pulley b, on to the larger cylinder at 
c. Now, when the winch is turned to raise the 
telescope, the endless cord is unwound from the 
smaller cylinder and wound on to the larger: the 
difference of the size of the two cylinders will be 
double the quantity raised, and a mechanical force 
to any extent may thus be obtained by duly pro- 
portioning the diameters of the two cylinders; by 
this contrivance the necessity for an assistant is 
superseded. The instrument, when not in use, is 
let down into the box d d, and covered with canvas, 
to prevent dust or moisture from tarnishing the 
speculum. 

The applications of the telescope to the purposes 
of man are so numerous, that their details would 
far exceed the boundaries of our treatise. Amongst 
its principal uses, however, besides those accom- 
panying the descriptions of the various modifications 
of that instrument, may be enumerated the follow- 
ing: — The accurate determination of the longitude 
of the various places on the earth's surface is 
ascertained by the telescope, by observing the 
immersions and emersions of the four satellites 
of the planet Jupiter ; thence, by the aid of a 
good chronometer, with the time of any known 
place, the situation of the unknown spot is deter- 
mined. Before the invention of the telescope, 
navigators were compelled to keep within sight 
of the coast in sailing from one country to another, 
and thus were often endangered while passing a 
hostile or rocky shore; by the assistance of this 
instrument, the voyage is made direct to the 
intended place without fear or danger. 

To the astronomer the telescope is his principal 
and most important guide. It enables him to de- 
termine with precision the transits of the planets 
and stars across the meridian. The computation 
of astronomical and nautical tables, to determine 
the revolution of the planets on their axes, and 
their relative polar and equatorial diameters, is 
derived from observations by the telescope. We 
are by this instrument enabled to discover the 



analogy between the laws which govern the mo- 
tions of the planets and those of our earth, their 
parallax, and thence their distances. The aber- 
ration of light, and the motions of the sidereal 
systems in space, unfold wonders which must excite 
the imagination of the most profound philosophers 
in the highest possible degree. The harmony and 
simplicity displayed in such immense worlds prove 
the design and wisdom by which they were created ; 
and the wonderful facts thus ascertained raise the 
most ordinary mind up to a sublime contemplation 
of the great Creator. 

In surveying land, the telescope is highly useful, 
and for this purpose is mounted on a stand, with 
a horizontal and vertical motion, registering, by 
divisions, the degrees and minutes of inclination 
or position of the instrument. For the more 
accurate reading off these divisions, the two limbs 
are furnished with a Vernier's scale. Spirit-levels 
and a magnetic needle are usually attached to the 
instrument ; and, from the purposes to which, it is 
applied, a telescope with this mounting is called a 
theodolite, derived from two Greek words meaning 
an instrument for seeing or determining distances. 
The method by which the distances and heights 
of remote objects are ascertained is by measuring 
the angles subtended by the object, and computing 
trigonometrically therefrom. 

Some writers have much exaggerated the powers 
and penetration of the telescope; indeed, it has 
been gravely asserted that works of art had been 
recognised in our satellite, the moon. The fallacy 
of this circumstance may be easily shown to our 
readers by the following simple considerations. 
Let a person direct the tubes of a telescope (with- 
out the glasses) to any celestial object, and there 
fix them ; he will soon find that in a short space 
of time the object will have removed from before 
the mouth of the tube. Now this motion of the 
celestial bodies, which is only apparent, arises from 
the revolution of our earth on its axis; and the 
quantity of this motion may be determined with 
facility thus: — the earth is known to revolve once 
about its axis in twenty-four hours ; and as every 
circle is supposed to be divided into three hundred 



WONDERS OF THE HEAVENS. 



309 



and sixty equal parts or degrees, the apparent 
time any celestial body takes to describe one 
degree will be found by dividing twenty-four hours 
by three hundred and sixty, which gives us four 
minutes as the time an object would pass the 
mouth of the tube if it only takes in one degree of 
the heavens. 

Now, if we suppose the glasses to be placed in 
the tubes, the magnifying power of the instrument 
being sixty, and we direct it (as before) to an 
object, as the moon, whose diameter is about half 
a degree, the time of her passing or transit will be 
one minute, if the field of view be, as in the ordi- 
nary telescopes, about thirty minutes, which the 
moon would exactly occupy. If the power of the 
telescope be increased ten times, the eye-piece 
having the same angle of vision, only a hundredth 
part of the moon would be seen at once, one 
hundred being the square of ten, the increased 
power of the instrument ; and the time in which 
this portion of the moon would pass the telescope 
is six seconds. Again, if we increase the power 
ten times, so that its linear amplification of an 
object is six thousand times, only a ten-thousandth 
part of the moon's surface could be seen in the 
field of view ; or the planet Saturn, whose apparent 
diameter is ten seconds, would just fill it, and the 
time of their passing the instrument would be only 
six-tenths of a second. 

Having thus shown the amazing velocity with 
which a planet passes the mouth of a telescope 
with these high powers, we shall next proceed to 
point out the apertures and amplification necessary 



for observing some given measure on the surface 
of the moon. First, we must determine the angle 
every object must subtend to the eye in order to 
render it visible : this is found on an average for 
different sights to be one minute ; that is, when an 
object is removed from the eye about three thousand 
times its own diameter it will only be just distin- 
guishable. From this we can now determine the 
extent of the smallest part of the moon's surface 
discoverable by the unassisted eye. Its real 
diameter is two thousand one hundred miles, 
which, divided by the number of minutes that 
its apparent diameter subtends, viz. thirty gives 
us seventy miles as the measure of the least dis- 
tinct spot seen by the naked eye; therefore we 
know that, if a telescope magnifies seventy times, 
we can just discern a spot one mile in diameter on 
the moon's surface ; and to recognise any object 
ten feet in diameter, we shall find by this rule 
the magnifying power of the telescope must be 
thirty-seven thousand one hundred times ; and the 
diameter of an object-glass or metal for such an 
instrument may also be found. If we suppose a 
pencil of rays one-fiftieth of an inch in diameter 
will admit suflScient light to the eye, the diameter 
of the speculum must be sixty-two feet, and its 
focal distance three hundred and nine feet, when 
an eye-glass of one-tenth of an inch is employed., 
These calculations must convince the reader of our 
inability to make such observations; for if the 
impossibility of procuring such enormous instru- 
ments were overcome, they would be so unwieldy 
as entirely to prevent our using them. 



CHAPTER X 



Zodiacal light — Observed by Cassini in 1683 — By Childrey previous 
to 1661— By others in 1707— By Professor Olmsted in 1834— 
Various theories — Aurora borealis — Appearances in the Shetland 
Islands — In Siberia — At Hudson's Bay— ^Sounds attending their 
appearance — Aurora seen by Capt. Ross — Southern lights observ- 
ed by Forster — Northern lights as seen in England, March, 1716 — 
Supposed height of these meteors — Theories respecting their cause 



— Halley's — Mairan's — Euler's — Franklin's — Kirwan's — Appear- 
ances in August and September, 1827 — December and November, 
1835— April, 1836. 

The Zodiacal Light is a pyramid of light which 
sometimes appears in the morning before sunrise, 



310 



WONDERS OF THE HEAVENS. 



and in the evening after sunset. It has the sun 
for its basis. Its sides are not straight, but a little 
curved, its figure resembling a lens edgewise. It 
is generally seen here about October and March, 
that being the time of our shortest twilight. It 
cannot be seen in the twilight, and when that 
lasts a considerable time, the zodiacal light is 
withdrawn before the twilight ceases. This light, 
which is something like the milky way, or that of 
a faint twilight, or like the tail of a comet, thin 
enough to allow stars to be seen through it, seems 
to surround the sun in the form of a lens, whose 
plane is nearly coincident with that of the sun's 
apparent path. It is seen stretched along the 
zodiac, and accompanies the sun in his annual 
course through the twelve signs; each end termi- 
nates in an angle of about twenty-one degrees; 
the extent in length from the sun to either of the 
angular points varies from fifty to one hundred 
degrees; it reaches beyond the orbit of Mercury, 
and probably of Venus ; the breadth of it near the 
horizon being also variable from twelve to thirty 
degrees; near the sun it cannot be seen. This 
light is weaker in the morning, when day is coming 
on, than at night, when darkness is increasing. At 
the equator it is visible all the year round. In 
high latitudes it may be best seen after evening 
twilight about the last of February, or before 
morning twilight at the beginning of October; 
because at these times it is nearly perpendicular 
to the horizon, and consequently clearer from the 
thick vapors near the horizon, and from the effects 
of a lingering twilight. It may be seen, but more 
dimly, during the whole of the winter. The figure 
in the right hand column represents the zodiacal 
light. 

It was observed by Cassini in 1683, a little 
before the vernal equinox, in the evening, extend- 
ing along the ecliptic from the sun. He thinks, 
however, that it had been seen before and after- 
ward disappeared, from an observation of J. Chil- 
drey, in a book published in 1661, in which may 
be found the following passage: — "In the month 
of February, for several years, about six o'clock in 
the evening, after twilight, I saw a path of light 



tending from the twilight toward the Pleiades, as 
it were touching them. This is to be seen when- 
ever the weather is clear, but best when the moon 




does not shine. I believe that this phenomenon 
has been before visible, and will hereafter appear, 
always at the above-mentioned period of the year ; 
but the cause and nature of it I cannot guess, and 
therefore leave it to the inquiry of posterity." 
This phenomenon may be what the ancients called 
trabes, (beams,) which word they used for an 
impression of light in the air. Des Cartes speaks 
of an appearance of the same kind. Fatio de 
Duillier observed it immediately after the discovery 
by Cassini, and suspected "that it had always 
appeared." It was soon after observed by Kirch 
and Eimmart in Germany. 

On the 3d of April, 1707, there was observed at 
Essex, England, in the western part of the heavens, 
about a quarter of an hour after sunset, a long 
slender pyramidal appearance perpendicular to the 



WONDERS OF THE HEAVENS 



311 



horizon. The sun seemed to be the base of this 
pyramid, and its apex reached twenty degrees 
above the horizon. It was throughout of a rusty 
red color, and quite vivid when first seen, but the 
upper part much fainter than the base. It became 
gradually weaker and weaker, so that in a quarter 
of an hour after it was first seen, its vertex was 
scarcely visible. The lower part remained vivid 
more than an hour, yet gradually decreasing in 
length all the time. The observer had never seen 
any thing like it, except the "pyramidal glade," 
which is now called the aurora borealis; it was 
like that, except in color and length. This was 
without doubt the zodiacal light. 

On the eleventh of October, 1834, Professor 
Olmsted's attention was attracted to the appearance 
of the zodiacal light in the morning sky. At that 
time it presented a pyramidal form, resting its 
broad base on the horizon, and terminating in a 
faint, indefinite extremity near the nebula in the 
constellation of the Crab. It was then asked 
whether this light has any connection with falling 
stars, and whether it would sustain any change on 
or about the 13th of November. The change 
contemplated was, that about that time it would 
pass by the sun and become visible in the evening 
sky after twilight. It was observed in the morning 
until after the 13th of November. As soon after 
that as the absence of the moon permitted, viz. on 
the 19th, the extreme parts of the same luminous 
pyramid were recognised in the west immediately 
after twilight ; but owing to the low angle made by 
the ecliptic with the western horizon at that time, 
the light was carried so near the horizon in the 
south-west as to have its distinctness much impair- 
ed; it could, however, be traced a little above the 
two bright stars in the head of Capricorn. From 
that time to the last of December it was seen, on 
every favorable evening, advancing, in the order of 
the signs, faster than the sun ; on the evening of the 
21st of December, in a peculiarly favorable state 
of the atmosphere, it was faintly discernible from 
six to seven o'clock, reaching nearly to the equi- 
noctial colure, and of course ninety degrees from 
the sun measured on the ecliptic ; it also continued 



visible in the morning sky, although evidently 
withdrawing to the other side of the sun. 

Fatio conjectured this appearance to be owing 
to a collection of corpuscles encompassing the sun 
and reflecting its light. Cassini at first supposed 
that it might arise from an infinite number of small 
planets revolving about the sun ; so that this light 
might owe its existence to these bodies, as the 
milky way does to an infinite number of fixed stars. 
He, however, soon rejected this for another solu- 
tion, viz. that it is caused by particles incessantly 
flying off" from the body of the sun, detached by 
the rotation of that luminary on its axis. The 
velocity of the equatorial parts of the sun, being 
the greatest, would throw the matter to the greatest 
distance; and on account of the diminution of 
velocity toward its poles, the height to which the 
matter would rise would be less ; and as it might 
spread a little sideways, it would assume the form 
of a lens or double cone, whose section, perpen- 
dicular to its axis, would coincide with the sun's 
equator. This is an ingenious theory; but there 
is one great difficulty in thus accounting for the 
phenomenon. It is well known to astronomers 
that the centrifugal force at the sun's equator must 
be a great many times less than its gravity ; it 
does not appear, therefore, how the sun from its 
rotation can detach any of its gross particles. If 
there be particles detached from the sun, they 
must be sent off" by some other unknown force ; in 
which case they would probably be sent off" in all 
directions equally, which would not give the zodia- 
cal light the figure it is observed to have. Brewster 
says, "It is settled that we may not regard this 
light as produced by a solar atmosphere, as the 
medium is of so rare a nature that it has no 
sensible eff"ect on the light of the heavenly bodies." 
But Herschel the younger, who has written more 
recently, and on whose opinion we are most dis- 
posed to rely, does not think it a matter decided 
this way, but rather the reverse. He says, "The 
zodiacal light is a phenomenon which seems to 
indicate some degree of nebulosity about the sun, 
and even to place that body in the list of nebulous 
stars. It is manifestly in the nature of a thin, 



r^ 



sssaasBsrajBM 



312 



WONDEUS OP THE HEAVENS. 



lenticularly-formed atmosphere surrounding the 
sun, and may be conjectured to be no other than 
the denser part of that medium, which, we have 
reason to believe, resists the motion of comets ; 
loaded, perhaps, with the actual materials of the 
tails of millions of those bodies, of which they have 
been stripped in their successive perihelion passages, 
and which may be slowly subsiding into the sun." 

AURORA BOREALIS. 

The northern light is an extraordinary meteor, 
or luminous appearance, showing itself in the night- 
time, in the northern part of the heavens, and 
usually in frosty weather. 

It is generally of a reddish color, inclining to 
yellow, and sends out frequent corruscations of 
pale light, which seems to rise from the horizon in 
a pyramidal undulating form, and shoots with great 
velocity up to the zenith. 

This kind of meteor, which is more uncommon 
as we approach the equator, is almost constant in 
the polar regions during the long winter of that 
climate, and appears there with the greatest lustre. 

In the Shetland Isles, the merry dancers, as they 
are there called, are the constant attendants of 
clear evenings, and afford great relief amidst the 
gloom of long winter nights. They commonly ap- 
pear at twilight near the horizon, of a dun color, 
approaching to yellow. They sometimes continue 
in that state for several hours, without any percep- 
tible motion, and afterward break out into streams 
of stronger light, spreading into columns, and 
altering slowly into ten thousand different shapes, 
and varying their colors from all the tints of yel- 
low to the most obscure russets. They often cover 
the whole hemisphere, and then they exhibit the 
most brilliant appearance. Their motions at this 
time are inconceivably quick, and they astonish 
the spectator Avith the rapid change of their form. 
They break out in places where none were seen 
before, skimming briskly along the heavens; are 
suddenly extinguished, and succeeded by a uniform 
dusky tract. This again is brilliantly illuminated 
as before, and as suddenly left a dark space. 
Some nights they assume the appearance of dark 



columns, on one side of the deepest yellow, and on 
the other gradually changing, till they become un- 
distinguishable from the sky. They have generally 
a strong tremulous motion from one end to the 
other, and this continues till the whole vanishes. 
As for us, who see only the extremities of these 
phenomena, we can have but a faint idea of their 
splendor and motions. According to the state of 
the atmosphere, they differ in color, and sometimes 
assuming that of blood, they present a terrific ap- 
pearance. The rustic sages who observe them 
become prophetic, and terrify the spectators with 
alarms of war, pestilence, and famine ; nor indeed 
were these superstitious presages peculiar to the 
northern islands. Appearances of a similar nature 
are of ancient date, and they were distinguished by 
the appellations of "phasmata," (sights,) "trabes," 
(beams,) and "bolides," (darts,) according to their 
different forms and colors. Pliny states that "out 
of the firmament there appeared at night a bright 
light at sundry times, rendering the night as bright 
as the day." In old times, however, they were 
more rare, or were less frequently observed; but 
when they were observed, they were supposed to 
portend great events, and the excited imagination 
formed of them aerial conflicts. 

In high northern latitudes these phenomena are 
not only singularly beautiful in their appearance, 
but afford travellers, by their almost constant efful- 
gence, a very beautiful light during the whole night. 
In Hudson's Bay they diffuse a variegated splendor 
which is said to equal that of a full moon. In the 
north-eastern parts of Siberia, according to the 
description of Gmelin, they are observed to begin 
with single bright pillars, rising in the north, and 
almost at the same time in the north-east, and, 
gradually increasing till they comprehend a large 
space of the heavens, rush about from place to 
place with inconceivable velocity, and finally almost 
cover the whole sky up to the zenith, and produce 
an appearance as if a vast tent was expanded in 
the heavens, glittering with gold, rubies, and sap- 
phire. A more beautiful spectacle cannot be 
painted; but whoever should see such a northern 
light for the first time, could not behold it without 



WONDERS OF THE HEAVENS 



313 



terror. For however fine the illumination may be, 
it is attended with such a hissing, cracking, and 
rustling noise through the air as if the largest fire- 
works were playing off. To describe what they 
then hear, the people say "spolochi chodjat," that 
is, "the raging host is passing." The hunters, 
who pursue the white and blue foxes on the con- 
fines of the Icy Sea, are often overtaken in their 
course by the northern lights. Their dogs are 
then so much frightened that they will not move, 
but lie obstinately on the ground till the noise has 
ceased. Clear and calm weather commonly fol- 
lows this kind of northern lights. This account 
has been confirmed by the uniform testimony of 
many persons who have spent part of several years 
in very high northern latitudes, and inhabited differ- 
ent countries, from the river Yenissei to the Lena. 
This region seems to be the true birthplace of the 
lights. A person who had resided seven years at 
Hudson's Bay, spoke with admiration of the fine 
appearance and brilliant colors of the auroras, and 
particularly of their rushing noise, which he had 
frequently heard, and he compared it to the sound 
produced by swiftly whirling a stick at the end of 
a string. A similar noise has been heard in 
Sweden. A person at Northampton, (England,) 
when the lights were remarkably bright, was con- 
fident that he heard a hissing or whizzing sound. 
Cavallo states that the crackling noise is distinctly 
audible, and that he has heard it more than once. 
Mr. Belknap, at Dover, New Hampshire, testified 
that he heard a noise of a similar kind, during the 
appearance of the northern light. The following 
is his letter to a friend on the subject, and dated 
the 31st of March, 1783. "Did you ever, in ob- 
serving the aurora, perceive a sound? I once 
looked upon the idea as frivolous and chimerical, 
having heard it at first from persons whose creduli- 
ty I supposed exceeded their judgment ; but, upon 
hearing it repeatedly asserted by others, whom I 
thought judicious and curious, I began to entertain 
an opinion in favor of it. 

" I was strengthened in this opinion about two 
years ago, by listening with attention to the flash- 
ing of a luminous arch, which appeared on a calm 

40 



frosty night, when I thought I heard a faint rustling 
noise like the brushing of silk. Last Saturday 
evening I had full auricular demonstration of the 
reality of this phenomenon. About ten o'clock, 
the hemisphere was all in a glow ; the vapors as- 
cended from all points, and met in a central one 
near the zenith. All the difference between the 
north and south parts of the heavens was, that the 
vapor did not begin to ascend so near the horizon 
in the south as in the north. There had been a 
small shower with a few thunder-claps and a 
bright rainbow in the afternoon, and there was a 
gentle western breeze in the evening, which came 
in flaws with intervals of two or three minutes. 
In these intervals, I could plainly perceive the 
rustling noise, which was quite distinguishable from 
the sound of the wind, and could not be heard ex- 
cept when the flaws subsided. The flashing of the 
vapor was extremely quick; whether accelerated 
by the wind or not, is beyond my power to say. 
But from the quarter where the greatest quantity 
of vapor seemed to be in motion, the sound was 
plainest, and that quarter was the eastern during 
my observation. The scene lasted about half an 
hour, though the whole night was as light as when 
the moon is in her quarter." 

Perhaps the most extraordinary northern light 
for regularity and beauty ever witnessed, was that 
seen at Lynn Regis, England, on the 5th of Sep- 
tember, 1718, at ten o'clock in the evening, when 
the appearance was as represented in the accom- 
panying figure. On the next evening, between 




eight and ten o^clock, several columns of light 
were observed like those represented in the same 



314 



WONDERS OF THE HEAVENS 



figure at a a, not so bright as the pyramids of the 
evening before, which were carried toward the 
west, while these were carried toward the east. 
The rays arose out of a seemingly black cloud, 
though there was in reality no cloud there, for the 
stars shone plainly, and the moon was very bright 
in the midst of the blackness. 

Captain Ross speaks of numerous northern lights 
witnessed by him while on his second voyage of 
discovery in the North Sea. One he particularly 
describes as follows : — " 1829, November 24th. 
There was a brilliant aurora to the south-west, 
extending its red radiance as far as the zenith. 
The wind vacillated on the following day, and 
there was a still more brilliant aurora in the 
evening, increasing in splendor till midnight, and 
persisting till the following morning. It consti- 
tuted a bright arch, the extremities of which 
seemed to rest on two opposed hills, while its 
color was that of the full moon, and itself seemed 
not less luminous, though the dark and some- 
what blue sky by which it was backed was a 
chief cause, I have no doubt, of the splendor of its 
effects. We can conjecture what the appearance 
of Saturn's ring must be to the inhabitants of that 
planet ; but here the conjecture was perhaps veri- 
fied, so exactly was the form and light of this arch 
what we must conceive of that splendid planet- 
ary appendage, when crossing the Saturnian hea- 
vens. It varied however, at length, so much as to 
affect this fancied resemblance, yet with an increase 
of brilliancy and interest. While the mass or den- 
sity of the luminous matter was such as to obscure 
the constellation of the Bull, it proceeded to send 
forth rays in groups, forming such angular points as 
are represented in the stars of jewelry, and illum- 
inating objects on land by their corruscations. 
Two bright nebulse of the same matter afterwards 
appeared beneath the arch, sending forth similar 
rays, and forming a still stronger contrast with the 
dark sky near the horizon. About one o'clock it 
began to break up into fragments and nebulae, the 
corruscations becoming more frequent and irregu- 
lar, until it suddenly vanished at four." 

Similar appearances, called southern lights, (au- 



roras australes,) were long ago observed toward 
the south pole, and their existence was confirmed 
by Mr. Forster, who asserts, that in his voyage 
round the world with Captain Cook, he observed 
them in high southern latitudes, though attended 
with phenomena somewhat different from those 
which are seen here. On February 17th, 1773, in 
south latitude 58° " a beautiful phenomenon (he says) 
was observed during the preceding night, which 
appeared again for several successive nights. It 
consisted of long columns of a clear white light, 
shooting up from the horizon to the eastward, 
almost to the zenith, and gradually spreading over 
the whole southern part of the sky. These col- 
umns were sometimes bent sideways at their upper 
extremities, and though in most respects similar to 
the northern lights of our hemisphere, yet they 
differed from the last in being always of a whitish 
color, whereas ours assume various tints, especially 
those of a fiery and purple hue. The sky was 
generally clear when they appeared, and the air 
sharp and cold, the thermometer standing at the 
freezing point." 

The periods of the appearance of the northern 
lights are very inconstant. In some years they 
occur very frequently, and in others they are more 
rare. It has been observed that they are more 
common about the time of the equinoxes than at 
other seasons of the year. 

On Tuesday the 17th of March, 1716, about 
dusk, (seven o'clock,) "not only in London, but in 
all parts of England" where the beginning of this 
wonderful phenomenon was seen, there arose very 
long, luminous rays, perpendicular to the horizon 
and extending to the zenith, out of what seemed a 
dusky cloud in the north-east part of the heavens. 
The edges of this cloud were tinged with a reddish 
yellow, as if the moon were hid behind it. The 
reddish cloud spread rapidly along the northern 
horizon to the north-west, and immediately sent 
forth rays from all parts, now here, now there, 
they observed no rule or order in their rising. 
Many of these rays seemed to unite near the zenith, 
forming there a crown, or image, that drew the 
attention of all spectators. Some said that it 



WONDERS OF THE HEAVENS 



315 



resembled the representation of glory with which 
painters surround the name of God in churches; 
others, those radiating stars that glitter on the 
breast of the nobility; others would have it like 
the flame of an oven reverberating and rolling 
against its arched roof; others, again, thought it 
more like that tremulous light which is cast against 
a ceiling when the sun's beams are reflected from 
the surface of agitated water ; but all agreed that 
this spectrum remained but a few minutes, and 
was variously tinged with colors, yellow, red, and 
green. The crown soon dispersed, and did not 
appear again. But still, without any order as to 
time, place, or size, luminous rays continued to 
rise perpendicularly, now in one spot, now in 
another; now longer, now shorter; now in quick 
succession, now few and far between. Nor did they 
arise, as at first, out of a cloud, but they often 
emerged at once out of the pure sky, which was 
more than ordinarily serene and still. Most of 
these rays ended in a point, and were shaped like 
erect cones ; others resembled the tails of comets 
so much that they might easily be mistaken for 
them. Some would continue visible for several 
minutes, but the greater number just showed them- 
selves and died away. Some had but little or no 
motion ; others moved from east to west under the 
pole, contrary to the motion of the heavens, by 
which means they would sometimes seem to rush 
together, at other times to fly from each other. 
After this sight had continued about one hour and 
a half, the rays became less numerous and less 
elevated ; but that diffused light which had illumi- 
nated the northern parts of the heavens gradually 
subsided, and settling on the horizon, formed the 
representation of a very bright twilight, out of 
which arose long beams of light, not exactly erect, 
but declining toward the south; these, ascending 
by a quick and undulating motion to a considerable 
height, vanished in a little time, while others, at 
uncertain intervals, supplied their places. At the 
same time, an exceedingly black and dismal cloud 
seemed to hang over that part of the horizon which 
was situated between the north-west and the east. 
Yet no cloud was there in reality, but only a 



serene sky, so remarkably pure and limpid that 
the stars shone brightly in it, and particularly a 
star in the tail of the Swan, then very near the 
horizon ; the great blackness being only in appear- 
ance, and caused by a contrast with the great light 
collected above it. But the light had now assumed 
a new form, that of two streaks lying in a position 
parallel to the horizon, with ill-defined edges ; 
they were each about a degree in breadth, the 
lower being eight or nine degrees high, the other 
four or five degrees above it; these remained 
immovable for some time, and their light was so 
great that a man might have read print of an 
ordinary size. After an interval, the northern end 
of the upper streak bent downward and joined to 
the end of the lower, so as to shut up on the north 
side a space which still continued open to the east. 
Not long after, there suddenly appeared within this 
space a great number of small columns, perpendicu- 
lar to the horizon, and extending from one streak 
to the other, which disappeared so quickly that the 
observer could not decide whether they rose from 
the under, or fell from the upper line; by their 
sudden changes they caused such an appearance 
as might well be considered by the superstitious as 
conflicts in the sky. About this time there sudden- 
ly appeared, low under the pole, and very nearly 
due north, three or four lucid spots like clouds, in 
the pure black sky. These, as they broke out at 
once, so, after a few minutes continuance, they 
disappeared as quick as if a curtain had been 
drawn over them. Not long after, in the space 
above the parallel lines of light, there was seen a 
large pyramid of light, like a spear sharp at the 
top, which seemed to reach the zenith, or beyond 
it. This moved, with an equable and not very 
slow motion, from the north-east, where it arose, to 
the north-west, where it disappeared, keeping a 
perpendicular position, and passing successively 
over all the stars of the Little Bear, and not 
eflfacing the smallest in the tail, such was the 
extreme rarity and transparency of the matter of 
which it consisted. This was about eleven o'clock 
at night. Soon after, (the two parallel streaks of 
light having faded away,) there was formed in the 



316 



WONDERS OF THE HEAVENS. 



north an arch extending from the north-east to the 
north-west ; it had very much the appearance of a 
rainbow, except that it was of one uniform color, 
viz. a flame color, inclining to yellow; beneath this 
arch the sky was very black, and appeared like a 
dark cloud to the eye, but with the telescope the 
small stars were visible, though so near the horizon. 
Above this arch were visible the rudiments of 
another and larger arch, with an interval of dark 
sky between them. The moon rose in the course 
of the night, but caused no perceptible change in 
these appearances, neither diminution nor increase 
of light, but, as before, at intervals the light seemed 
to undulate and sparkle, not unlike the rising of 
the vaporous smoke of a great blaze when agitated. 
The following figure in some faint measure exhibits 




the appearances that have been described. A B is 
the lower streak of light, somewhat brighter than 
the upper, C D. Near its lower edge appeared 
Vega of the Harp ; and the bright star in the 
Swan's tail was below its northern extremity, (on 
the left.) All that region of the heavens was 
unusually black, as if all the light had been ab- 
stracted to form those bright parallel lines ; only 
at Q, between the west and north-west, there was 
the luminous bow, and the conical beams M L N 
arising out of it. In the mean time luminous spots 
G, G, G, G broke out from the clear sky. They 
did not break forth together, but successively ; yet 
two, or even three, might have been seen together. 
F, F, F, &c. are the small perpendicular columns. 
Lastly, from above the middle of C D arose the 
obelisk of light at H, which moved from east to 



west till it reached K in the north, and there 
disappeared. In accounting for these phenomena, 
Dr. Halley broaches a singular notion, which was 
supposed to have originated with one of our own 
countrymen,* and which was, a few years since, a 
subject of universal discussion, and of almost uni- 
versal ridicule. We shall quote Halley's own 
words: — "Supposing the earth to be concave, with 
a lesser globe included, then, in order to make that 
inner globe habitable, there might not improbably 
be contained some luminous medium between the 
balls, so as to make a perpetual day below. And if 
such a medium is inclosed within, what should 
hinder us from supposing that some of this lucid 
substance may, on rare and extraordinary occa- 
sions, transude through and penetrate the shell 
of our globe, and being loose, present us with the 
phenomena above described. This seems favored 
by one circumstance, the figure of the earth ; for 
that being a spheroid flattened at the poles, the 
shell must be thinner at the poles than in any other 
part, and therefore more likely to give passage to 
these vapors; whence a reason is derived for the 
light being always seen in the north," 

We have accounts of similar appearances of the 
northern light, occurring more than one hundred and 
fifty years previous to the above ; viz. in January, 
1560, October, 1564, in 1574, and twice in 1575. 
Probably, too, (as is intimated by Halley,) the 
descriptions of armies doing battle in the sky may 
nearly all of them have been the exaggerated 
accounts of superstitious or excited imaginations, 
alarmed by the peculiar appearances of the northern 
lights. Halley was unable to determine the height 
of this aurora, for want of contemporary observa- 
tions at other places ; although it was visible from 
the west of Ireland to the confines of Russia, and 
the east of Poland, extending nearly thirty degrees 
of longitude, and from about the fiftieth degree of 
north latitude over almost all the north of Europe ; 
and in all places at the same time it exhibited 
appearances similar to those above described. 
Boscovich calculated the height of an aurora in 
1737 to have been eight hundred and twenty-five 

* John Cleves Symmes. 






WONDERS OF THE HEAVENS 



317 



miles. Bergman, from a mean of thirty computa- 
tions, placed the average height at four hundred 
and sixty-eight miles. Euler supposed the height 
to be several thousand miles. Dr. Blagden, speak- 
ing of the height of some fiery meteors, says that 
"the northern lights appear to occupy as high, if 
not a higher region above the surface of the earth, 
as may be judged from the very distant countries to 
which they have been visible at the same time." 
He adds that "the great accumulation of electric 
matter seems to lie beyond the verge of our atmo- 
sphere, as estimated by the cessation of twilight." 
However, the height of these meteors, none of 
which appear to have ascended so high as one 
hundred miles, is trivial compared with the eleva- 
tions above ascribed to the northern lights ; but as 
it is difficult to make such observations on this 
phenomenon as are sufficient to afford a just 
estimate of its altitude, they must be subject to 
considerable variations and to material error. It 
is not improbable that the highest regions of the 
northern lights are the same as those in which 
fire-balls move; more especially as Dr. Blagden 
informs us that instances are recorded in which 
these lights have been seen to join and form 
luminous balls, darting about with great velocity, 
and even leaving a train behind like the common 
fire-balls. 

Many attempts have been made to assign a cause 
for the phenomena. Halley, among other theories, 
supposed that the watery vapors or eflluvia, rare- 
fied exceedingly by subterraneous fires, and tinged 
with sulphureous streams, which many naturalists 
have imagined to be the cause of earthquakes, 
might have been the cause of this appearance also. 
But this hypothesis was not sufficient to account for 
the immense extent of these phenomena over the 
surface of the earth. Abandoning this hypothesis, 
he conceived that the lights are produced by a 
subtil matter, or magnetic effluvia, freely pervad- 
ing the pores of the earth, and which, entering at 
its southern pole, passes out again with a like force 
into the ether near the northern pole, the obliquity 
of its direction being proportionate to its distance 
from the pole. This subtil matter, by becoming 



more dense, or having its velocity increased, may 
be capable of producing a small degree of light, 
after the manner of efltluvia from electric bodies, 
which, by a strong and quick friction, emit light in 
the dark ; to which sort of light this seems to have 
a great affinity. If Halley had known that an 
electrical stroke would give polarity to a needle, 
and reverse the poles of one already magnetic, he 
would have probably been led to conclude that the 
electric and magnetic effluvia were the same, and 
that the aurora borealis was this fluid, circulating 
from one pole of the earth to the other ; and thus 
he would have anticipated the theory of Beccaria. 

Mairan assigns as the cause of the aurora bore- 
alis the zodiacal light, which, according to him, is 
no other than the atmosphere of the sun. This 
light, happening on some occasions to meet the 
upper part of our air, on the side of the limits 
where universal gravity begins to act more forcibly 
toward the earth than toward the sun, falls into 
our atmosphere, to a greater or less depth as its 
specific gravity is greater or less compared with 
the air through which it passes. Although the 
whole atmosphere of the earth be involved in the 
solar atmosphere, it is thrown off" both ways from 
the equatorial to the polar regions. According to 
this theory, however, the light should dart from 
the equator to the poles, and not, as it really does, 
from the poles toward the equator. 

Euler thought the cause of the northern light 
not owing to the zodiacal light, but to particles of 
our atmosphere driven beyond its limit by the im- 
pulse of the sun's light. He supposes the zodiacal 
light and the tails of comets to be owing to a simi- 
lar cause. 

Ever since the identity of lightning and of the 
electric matter has been ascertained, philosophers 
have been naturally led to seek an explanation of 
aerial meteors in the principles of electricity ; and 
there is now little doubt that most of them, and 
particularly the northern lights, are electrical phe- 
nomena. Beside the more obvious and known ap- 
pearances which constitute a resemblance between 
this meteor and the electric matter whereby light- 
ning is produced, it has been observed that the 



318 



WONDERS OF THE HEAVENS 



aurora occasions a very sensible fluctuation in the 
magnetic needle; that the atmosphere yields, at 
the time of its occurrence, a quantity of electric 
fire; and that when it has extended lower than 
usual into the atmosphere, the flashes have been 
attended with various sounds of rumbling and hiss- 
ing already mentioned, and attributed by Dr. Blag- 
den to small streams of electric matter running off" 
to the earth from the great masses or accumulations 
of electricity by which he supposes both meteors 
and the northern lights are produced. Besides, 
the last may be partly imitated by means of artifi- 
cial electricity. 

Hamilton, of Dublin, seems to have been the first 
person who attempted to discover any positive evi- 
dence of the electrical quality of the northern 
lights, but the only proof he produces is an exper- 
iment of Hawksbee by which the electrical fluid is 
shown to assume appearances resembling those 
lights, when it passes through a vacuum. When 
the air was most perfectly exhausted, the streams 
of electric matter were quite white; but when a 
small quantity of air was let in, the light assumed 
more of a purple color. The flashing of this light, 
therefore, from the dense regions of the atmosphere 
into such as are more rare, and the transition 
through media of different density, he considers as 
the cause of the aurora borealis, and of the differ- 
ent colors it assumes. Mr. Canton, soon after he 
had obtained electricity from the clouds, offered a 
conjecture that the northern lights are occasioned 
by the flashing of electric fire from positive towards 
negative clouds at a great distance, through the 
upper part of the atmosphere, where the resist- 
ance is least. And he supposes that the aurora 
which happens at the time when the magnetic 
needle is disturbed by the heat of the earth, is 
the electricity of the heated air above it; and 
this appears chiefly in the northern regions, as the 
alteration in the heat of the air in those parts will 
be the greatest. Nor is this hypothesis, he says, 
improbable, when it is considered that electricity is 
the known cause of thunder and lightning ; that it 
has been extracted from the air at the time of the 
appearance of northern lights ; that the inhab- 



itants of the northern countries observe it to be 
remarkably strong w^hen a sudden thaw succeeds 
severe cold weather; and that the tourmalin is 
known to emit and absorb the electric fluid only by 
the increase or diminution of its heat. Positive 
and negative electricity in the air, with a proper 
quantity of moisture to serve as a conductor, will, 
he conceives, account for this and other meteors 
sometimes seen in a serene sky. Canton afterward 
contrived to exhibit this meteor by means of a 
vacuum in a glass tube about three feet long, and 
hermetically sealed. When one end of the tube is 
held in the hand, and the other applied to the con- 
ductor, the whole tube will be illuminated, and will 
continue luminous without interruption for a consid- 
erable time after it has been removed from the con- 
ductor. If after this it be drawn through the hand 
either way, the light will be uncommonly intense, 
and without interruption from one end to the other 
through its whole length. And though a great part 
of the electricity is discharged by this operation, it 
will flash at intervals, when held only at one ex- 
tremity, and kept quite still ; but if it be grasped 
by the other hand at the same time in a different 
place, strong flashes of light will scarcely ever fail 
to dart from one end to the other, and will continue 
to do so twenty-four hours and longer, without any 
fresh excitation. To Canton's hypothesis it has 
been objected that the electrical fire would flash in 
every direction, according to the position of the 
clouds, as well as from north to south, and that by 
the illustration of the tourmalin, the northern light 
ought to be most frequent in summer, whereas the 
reverse is true. Beccaria conjectured that there 
is a constant and regular circulation of the electric 
fluid from north to south, which may be the original 
course of magnetism in general, and that the 
northern lights may be this electric matter per- 
forming its circulation in such a state of the atmo- 
sphere as renders it visible on approaching the 
earth nearer than usual. 

Why the electricity of the atmosphere should be 
constantly found to direct its course from the poles 
toward the equator, and not from the equator to- 
ward the poles, gives rise to a difficulty that has 



^ 



miw^nww.;uii].wniiWBi wwatw 



WONDERS OF THE HEAVENS. 



319 



been answered by a writer in the following manner. 
Assuming three axioms, viz. that all electric bodies 
when considerably heated become conductors ; that 
therefore non-electrics, when subjected to violent 
degrees of cold, ought to become electric ; and that 
cold must increase the electric powers of such sub- 
stances as are already electric; it is easy (says this 
writer) to deduce from these principles the cause 
of the northern lights. The air, all round the 
globe, at a certain height above its surface, is found 
to be exceedingly cold, and, as far as experiments 
have yet determined, exceedingly electrical also. 
The inferior parts of the atmosphere between the 
tropics are violently heated during the day by the 
reflection of the sun's rays from the earth. Such 
air will therefore be a kind of conductor, and much 
more readily part with its electricity to the clouds 
and vapors floating in it, than the colder air toward 
the north and south poles. Hence the electricity 
in these regions is exhibited in thunder and tem- 
pests of the most terrible kind. Immense quantities 
of the electric fluid are thus communicated to the 
earth, and the inferior warm atmosphere, having 
once exhausted itself, must necessarily be recruited 
from the upper and colder regions. This is very 
probable from what the French mathematicians 
observed on the top of the Andes. They were 
often involved in clouds, which, sinking down into 
the warmer air, appeared there to be highly elec- 
trified, and discharged themselves in violent tem- 
pests of thunder and lightning ; while in the mean 
time, on the top of the mountain, they enjoyed a 
calm and serene sky. In the temperate and frigid 
zones, the inferior parts of the atmosphere, never 
being so strongly heated, do not part with their 
electricity so easily as in the torrid zone, and 
therefore do not require such recruits from the 
upper regions; and though a great difference is 
observable in different parts of the earth near the 
surface, it is very probable that at considerable 
heights the degrees of cold are nearly equal all 
round it. Were there a like equality in the heat 
of the under part, there never could be any con- 
siderable loss of equilibrium in the electricity of 
the atmosphere ; but as the hot air of the torrid 



zone is perpetually bringing down vast quantities 
of electric matter from the cold air that lies directly 
above it, and as the inferior parts of the atmo- 
sphere lying toward the north and south poles do 
not bring it down in any quantities, it follows that 
the upper parts of the air lying over the torrid 
zone will continually require a supply from the 
northern and southern regions. This shows the 
necessity of an electric current in the upper parts 
of the atmosphere from each pole toward the 
equator. We are thus also furnished with a reason 
for the northern lights appearing more frequently 
in winter than in summer, because at the former 
season the electric power of the inferior atmo- 
sphere is greater, owing to cold, and consequently 
the abundant electricity of the upper regions must 
go almost wholly off" to the equatorial parts, it 
being impossible for it to get down to the earth; 
hence also the northern lights appear very frequent 
and bright in the frigid zones, the degrees of cold 
in the upper and lower regions of the air being 
more nearly equal in those parts than in any other. 
In some parts of Siberia, this meteor appears con- 
stantly from October to January, and its corrusca- 
tions are said to be quite terrifying. Travellers 
agree that the northern lights appear there in the 
greatest perfection. From experiments made with 
the electrical kite, the air appears more electrical 
in winter than in summer, though the clouds are 
known to be often most violently electrified in the 
summer-time ; a proof that the electricity naturally 
belonging to the air is in summer more powerfully 
drawn oflf by the clouds than in the winter, owing 
to the excess of heat in the former season. 

Still, according to the above hypothesis the 
streams of light ought to run from north to south, 
instead of ascending, as they are generally suppos- 
ed to do. Dr. Halley answered this difficulty by 
supposing that the magnetic effluvia pass from pole 
to pole in arcs of great circles, arising to a very 
great height above the earth, and consequently 
darting from the places whence they arose almost 
like the radii of a circle, in which case, setting off" 
in a direction nearly perpendicular to the surface 
of the earth, they must necessarily appear erect to 



320 



WONDERS OF THE HEAVENS 



those who see them from any part of the surface, 
as is demonstrated by mathematics. It is also 
reasonable to think that they will take this direc- 
tion rather than any other, on account of their 
meeting wnth less resistance in the very high re- 
gions of the air than in such as are lower. We 
have supposed the equilibrium of the atmosphere 
to be broken in the day-time and restored only in 
the night; whereas, considering the immense ve- 
locity with which the electric fluid moves, the 
equilibrium ought to be restored in all parts almost 
instantaneously, yet the northern lights appear 
only in the night, although their brightness is such 
as must sometimes make them visible to us, did 
they really exist in the day-time. In answer to 
this, it may be observed that though the passage of 
electricity through a good conductor is instantane- 
ous, yet through a bad conductor it takes some 
time in passing. Now as our atmosphere, unless 
violently heated, is a bad conductor of electricity, 
when the equilibrium is once broken it cannot be 
instantaneously restored. Besides, it is the action 
of the sun that breaks the equilibrium, and the 
same action, extending over half the globe, prevents 
almost any attempt to restore it till night, when 
flashes arise from various parts of the atmosphere, 
gradually extending themselves with a variety of 
undulations towards the equator. 

It has been observed that the streams do not 
always move with rapidity, but sometimes appear 
quite stationary for a considerable time, and are 
sometimes carried in different directions with a 
slow motion. In order to account for these cir- 
cumstances, we should consider that weak electric 
lights h^e been known sometimes to exhibit the 
same appearance at the surface of the earth ; and 
we may therefore suppose them much more capa- 
ble of doing so at great heights above, where the 
conductors are much more imperfect, and fewer in 
number. We may reasonably conclude, from in- 
stances which have taken place, that small por- 
tions of our atmosphere may, from various causes, 
be so much electrified as to shine and be moved 
from one place to another, without parting with the 
electricity they have received, for a considerable 



time. In this way we may account for the crown 
or circle which is often formed near the zenith by 
the northern lights, when any of its parallel 
streams of light, that shoot upward, and (by the 
laws of perspective) appear to converge toward a 
point, are over our heads, and actually come to a 
point. As this crown is commonly stationary for 
some time, it would serve as a mark by which to 
determine the distance of the object ; for example, 
let two persons, one at Washington and one at 
Boston, observe the bearing of the crown from 
their respective positions, its true altitude from the 
surface of the earth might be determined by 
trigonometry. Although the streams may resemble 
the passage of electric light through a vacuum, it 
cannot be hence inferred that the air is in a state 
similar to the vacuum of an air-pump in those 
places where the northern lights are produced, 
because there are instances of similar appearances 
that are produced in very dense air. 

The plate of an electrophorus is often so highly 
electrified as to throw out flashes from different 
parts as soon as it is lifted up, and by proper man- 
agement it may be always made to emit long and 
broad flashes, which shall scarcely be felt by the 
finger, instead of small dense and pungent sparks ; 
so that, though long flashes may be produced in 
rarefied air, it does not follow that the same may 
not be produced also in denser air. Little, the in- 
ventor of one variety of the air-pump, conceived 
that the northern lights could not appear in air less 
rarefied than four thousand times, and consequent- 
ly that its least distance from the earth is about 
forty-five miles ; and that in air rarefied more than 
twenty-six, thousand times it would not be visible, 
and therefore its greatest distance is about fifty 
miles. He thinks, also, that it is air burnt and 
exploded in its passage which makes the electric 
matter visible, and that without air, if it could 
pass at all, it would not be luminous. Upon the 
whole, he concludes that the northern lights are 
within our atmosphere. 

Our Franklin supposes that the electrical fire 
discharged into the polar regions from many leagues 
of vaporized air raised from the ocean between 



WONDERS OF THE HEAVENS 



321 



the tropics, accounts for the northern lights, and 
that they appear first where it is first in motion, 
viz. in the most northern part, and the appearance 
proceeds southward, though the fire really move 
northward. 

His reasoning is this : — Air heated by any nieans 
becomes rarefied, and specifically lighter than any 
other in the same situation not heated; when 
lighter it rises, and the neighboring cooler and 
heavier air takes its place. If in the middle of a 
room you heat the air by a stove or vessel of 
burning coals near the floor, the heated air will 
rise to the ceiling, spread over the cooler air till 
it comes to the cold walls, where, being condensed 
and made heavier, it descends to supply the place 
of the heated air which had ascended toward the 
ceiling. Thus there will be a continual circulation 
of air in the room, which may be made evident by 
setting free a little smoke, for that smoke will rise 
and circulate with the air. 

A similar operation is performed by nature on 
the air of the globe. Above the height of our 
atmosphere the air is so rare as to be almost a 
vacuum. The air heated between the tropics is 
continually rising ; its place is supplied by northerly 
and southerly winds, which come from the cooler 
regions. The light, heated air, floating above the 
cooler and denser, must spread northward and south- 
ward, and descend near the two poles, to supply 
the place of the cool air which had moved toward 
the equator. Thus a circulation of air is kept up in 
our atmosphere, as in the room above-mentioned. 

The great quantity of vapor rising between the 
tropics forms clouds, which contain much electrici- 
ty ; some of them fall in rain before they come to 
the polar regions. Every drop brings down some 
electricity with it ; the same is done by snow and 
hail ; the electricity so descending, in temperate 
climates, is received and imbibed by the earth. If 
the clouds are not sufficiently discharged by this 
gradual operation, they sometimes discharge them- 
selves suddenly by striking into the earth where 
the earth is fit to receive their electricity. The 
earth in temperate and warm climates is generally 

fit to receive it, being a good conductor. 

41 



The humidity contained in all the equatorial 
clouds that reach the polar regions, must there be 
condensed and fall in snow. The great cake of 
ice that eternally covers those regions may be too 
hard frozen to permit the electricity descending 
with that snow to enter the earth ; it may there- 
fore be accumulated upon the ice. The atmo- 
sphere, being heavier in the polar regions than in 
the equatorial, will there be lower, as well from 
that cause, as from the smaller effect of the cen- 
trifugal force; consequently the distance of the 
vacuum above the atmosphere wnll be less at the 
poles than elsewhere, and probably much less than 
the distance from the pole to those latitudes in 
which the earth is so thawed as to receive and 
imbibe electricity. May not then the great quan- 
tity of electricity brought into the polar regions by 
the clouds — electricity which would enter the earth, 
but cannot penetrate the ice — may it not, as in a 
bottle overcharged, break through that low atmo- 
sphere, and run along in the vacuum over the air 
toward the equator, diverging as the degrees of 
longitude, strongly visible where densest, and be- 
coming less visible as it diverges more, till it finds 
a passage to the earth in more temperate climates, 
or is mingled with the upper air? If such an ope- 
ration of nature were really performed, would it 
not give all the appearances of the northern lights? 
And would not these become more frequent after 
the approach of winter, not only because more 
visible in longer nights, but also because in summer 
the long presence of the sun may soften the surface 
of the great ice-cake and render it a conductor, by 
which the accumulation of electricity in the polar 
regions will be prevented ? 

The atmosphere of the polar regions being made 
more dense by the extreme cold, and all the moist- 
ure in that air being frozen, may not any great 
light arising therein and passing through it, render 
its density in some degree visible during the night- 
time to those who live in the rarer air of more 
southern latitudes ? And would it not in that case, 
although in itself a complete and full circle, ex- 
tending perhaps ten degrees from the pole, appear 
to spectators (so placed that they could see only a 



322 



WONDERS OF THE HEAVENS. 



part of it) in the form of a segment, its chord 
resting on the horizon, and its arch elevated more 
or less above it, as seen from latitudes more or less 
distant ; darkish in color, but yet sufficiently trans- 
parent to permit some stars to be seen through it ? 

The rays of electric matter issuing out of a body 
diverge by mutually repelling each other, unless 
there be some conducting body near to receive 
them; and if that conducting body be at a great 
distance, they will diverge, and then converge in 
order to enter it. May not this account for some 
of the varieties of figures seen at times in the 
motions of the luminous matter of the aurora, since 
it is possible that, in passing over the atmosphere 
from the north in all directions towards the equa- 
tor, the rays of that matter may find, in many 
places, portions of cloudy region or moist atmo- 
sphere which may be fit to receive them, and 
toward which they may therefore converge ; and 
when one of these receiving bodies is saturated, 
they may again diverge from it toward other sur- 
rounding masses of such moist atmosphere, and 
thus form the crowns or other figures mentioned 
in the histories of this meteor. 

Kirwan supposes that the rarefaction of the 
atmosphere in the polar regions proceeds from the 
northern and southern lights, and that these are 
produced by a combustion of inflammable air caused 
by electricity. This inflammable air is generated, 
particularly between the tropics, by many natural 
operations, such as the putrefaction of animal and 
vegetable substances, volcanoes, &c., and being 
lighter than any other air, occupies of course the 
highest regions of the atmosphere. Kirwan adds, 
that after the appearance of the northern lights 
the barometer commonly falls, and that it is gener- 
ally followed by high winds, proceeding usually 
from the south ; all which facts strongly prove a 
rarefaction in the northern regions. It has been 
observed also by another writer, that the appear- 
ance of the northern lights is a certain sign of a 
hard gale of wind from the south or south-west. 
This occurred without fail in twenty-three instan- 
ces ; and he thinks that the splendor of the meteors 
will enable the observer to form some judgment 



concerning the ensuing tempest. If the aurora is 
bright, the gale will come on in twenty-four hours, 
but will be of no long duration; if the light is 
faint and dull, the gale will be less violent, and 
longer in coming on, but will last longer. 

That the northern lights ought to be succeeded 
by winds, may be easily deduced from the hypoth- 
esis above-mentioned. If this phenomenon is oc- 
casioned by the vast quantity of electric matter 
conveyed to the equatorial parts of the earth, it is 
certain that the earth cannot receive any great 
quantity of this matter at one place without emit- 
ting it at another. The electricity, therefore, 
which is constantly received at the equator, must 
be emitted nearer the poles, in order to perform its 
course ; otherwise there would not be a constant 
supply of it for the common operations of nature. 
It is to be observed, that electrified bodies are 
always surrounded by a blast of air, sent forth from 
them in all directions ; hence if the electric matter 
find a more ready passage through one part of the 
earth than another, a wind will be found to blow 
from that quarter. The electric matter which had 
been received at the equator during an aurora, will 
be discharged at this part sometime after, and a 
wind will blow from that quarter. All the matter, 
however, will not probably be discharged at one 
spot, and therefore, according to the situation of 
these electrical vents, winds may blow in different 
directions. 

We shall conclude with certain accounts of re- 
cent appearances of northern lights, which have 
been represented as exceedingly brilliant and 
beautiful, but, when compared with the general 
description of these phenomena given above, will 
be found not to exceed the common appearance. 

On August 28th, 1827, the aurora borealis was 
generally seen in the northern states, in most of 
which there were no material variations in its ap- 
pearance. In the city of New York it was first 
observed at about half past nine in the evening, at 
which time the light, excepting in color, resembled 
that produced by a fire at some distance. It how- 
ever soon became more intense, and its outline 
more distinctly defined. It gradually assumed a 



WONDERS OF THE HEAVENS 



columnar shape, and extended from about north- 
north-west to the opposite point of the horizon. In 
ten or fifteen minutes, waves of light in detached 
masses began to flow from the eastern toward the 
western part of its course, until the whole were 
blended, and the heavens adorned with a beautiful 
arch. The greatest breadth of this arch was nine 
or ten degrees. The whole arch moved with a 
gradual and nearly uniform motion toward the 
south, and passed the zenith at about three quar- 
ters past ten, presenting to the eye through its 
whole length a broad, bright band of wavy light, 
studded with stars that were distinctly visible 
through it. The eastern limb became less dis- 
tinct, but the western more exact in its outline, and 
as well defined as a pencil of rays passed through 
a prism into a dark room. The color was a bright 
white. A great bank of light lay almost perma- 
nently in the northern horizon, sometimes sur- 
mounted by, and sometimes resting upon, what 
seemed a black cloud, visible during the whole 
phenomenon. Occasionally broad flashes of the 
aurora would illuminate the apparent cloud, pre- 
senting an appearance of a black thunder-cloud 
penetrated by vivid lightnings. 

At Gosport, about nine o'clock on the evening 
of September 25th, 1827, a bright yellow light ap- 
peared in the north-west quarter, behind a low 
stationary cirrostratus or wane-cloud, and gradually 
extended from the north toward the west nearly 
seventy degrees. At ten, it had a brighter appear- 
ance than the strongest twilight that appears in this 
latitude. At half past ten, the aurora had formed 
a tolerably well defined arch of intense light, and at 
quarter before eleven, perpendicular lucid columns 
and vivid corruscations appeared in quick succes- 
sion. At eleven, the streamers reached eight or 
nine degrees above the Pole-star, and their appa- 
rent base was nearly horizontal with the star Beta 
in the Great Bear. Soon after eleven, a column of 
light six degrees in width gradually rose from the 
position of the fore-mentioned star, and when it had 
reached an altitude of seventy degrees, it changed 
its color to a blood-red, which, with the more vivid 
and elevated flashes, gave the aurora an awfully 



grand appearance that it would be difficult to paint 
or express. This wide column increased in bril- 
liancy, and passed through the gradation of colors 
that is sometimes seen in the clouds near the hori- 
zon at sunset, as lake, purple, light crimson, &c. 
Two other columns of light, similar in color and 
width, soon sprang up in different directions, and 
passed the zenith several degrees to the southward. 
These three large variegated columns presented a 
very grand appearance. At one o'clock, lofty per- 
pendicular columns emanated from the aurora at 
the western point, and the northern hemisphere 
was filled with long and short streamers, varying 
in width and brilliancy, and often terminating in 
very pointed forms. 

The aurora in high northern latitudes, when at 
its extreme, is almost dazzling, and the quick- 
ness of its motions approaches to that of lightning. 
In other situations it has been observed to be vari- 
ously colored. 

But although all these combined are eminently 
wonderful, and strike the spectator with profound 
admiration and awe, yet perhaps regions of lower 
latitude exhibit, though not so splendid and varied 
a display of this mystery, one equally or perhaps 
more interesting to the philosopher. During the 
winter months, on Lake Ontario, the aurora may be 
said to be almost a constant companion of the dark 
and cheerless nights, and it occasionally presents 
itself at other times of the year. Nor is it in win- 
ter a mere display of a glorious phenomenon, the 
utility of which has not yet been exemplified by 
science, for it sheds a continued and pleasing light, 
which resembles the twilight. This light does not, 
as in Europe, emanate from the vivid streamers 
which dance over the starry floor of heaven in ever- 
changing and inexplicable mazes, but proceeds 
from the horizon, over which a pale luminous and 
depressed arch, embracing an extent of from sixty to 
ninety degrees, is commonly thrown. This arch is 
generally luminous in its whole body, not on the 
rim or verge only, which fades away into ethereal 
space, but from its superior circumference to the 
chord formed by the horizon itself, and varies in its 
elevation from ten to twenty degrees. Wherever 



324 



WONDERS OF THE HEAVENS 



it embraces stars, these are either veiled or dimly 
seen, being strongly contrasted with their fellow 
orbs of the southern heavens, which appear to 
shine out with the greater brilliancy. Within the 
space comprehended by this arch of light continual 
changes are operating, if the lights assume a 
splendid shape. Dark volumes of vapor, not like 
clouds, but blackening in a moment, rise and fall 
whenever a ray or an interior arch begins to form, 
and it is remarkable that this darkness usually ac- 
companies the commencement of every change, 
thereby increasing the majesty and beauty, as well 
as the brilliancy of the scene. But it is impossible 
for any pen adequately to describe a phenomenon 
which is continually presented in these regions, 
and it will be more satisfactory to detail the cir- 
cumstances attending one of the most beautiful of 
those seen at Kingston, U. C, during the winter of 
1835. 

On the 11th of December, after the sun had set, 
the sky was dark and gloomy, and although there 
were but few clouds visible, and the stars were 
rapidly brightening, a change of weather was ap- 
parent. 

The first appearance of the northern lights, after 
darkness had completely set in, was by the lumi- 
nous arch above-mentioned assuming its wonted 
place. From this arch, in the north, arose, almost 
incessantly, streamers of bright white light, which 
shot upward to the zenith, and streaked the dark 
sky with their silvery lines. Once a mass of light 
suddenly opened in the zenith, and from it darted 
out innumerable pencils of bright rays, overspread- 
ing the dark vault of heaven with their glories, and 
seeming for a moment to illuminate the sky with a 
star which its space seemed scarcely capable of 
containing. Again rods of white light would dart 
forth from the horizon, and one in particular span- 
ned the whole arch of heaven. This play of the 
northern lights continued from seven till nearly 
nine, and was most brilliant and magnificent about 
nine, when it assumed another and not less singu- 
lar attitude, of which the following is a faint delin- 
eation. 

These arches are not so flat as they should be. 



The lower one was usually the boundary of a very 
black, changing mass ; between the lower and the 




second arch the space was not so dark ; and be- 
tween the middle and upper arch it was still lighter, 
excepting where the corruscations shot upward 
from the middle arch, and there it was very dark. 
The ray shooting up on the right was extremely bril- 
liant. Stars were partially visible above the upper 
arch, but the bright ones in the Great Bear had 
lost all their splendor, and the constellation could 
just be traced. This obscuration of the heavenly 
bodies reached nearly to the zenith above the 
centre of the arch, but was less over the extremi- 
ties. After a short time the appearance became 
changed, and the aurora assumed the form shown 
in the following figure. The lower arch had some- 




what heightened and become darker, with here and 
there spots of light in it, whilst from its circumfer- 
ence shot out brilliant rays and pencils of light. 
The second arch had altogether disappeared, but 
the upper held its accustomed place. The upper 
arch was constantly paler and more indistinct in 



tf^ 



WONDERS OF THE HEAVENS 



325 



its outline than the others. Faint stars now ap- 
peared through the vapor, between the two arches, 
and the lower band became indistinct, excepting to 
the left of its central space, where it was extreme- 
ly well defined by a band of bright light cut off, 
both above and below, by black vapory masses. 
After another interval the aurora assumed a some- 
what different form. Both arches became less 




distinct; the lower one was almost obliterated, but 
its place was well marked by the arch of vapor 
below, which was darker than ever. Three large 
spots of intense light were now to be seen, one on 
the horizontal chord, and one on each side of the 
lower arch ; and the lower zone shot out innumer- 
able pencils and floods of light from its dark 
nucleus, the upper zone also darting forth long 
lines of brilliant rays ; all these rays moved in a 
stately march from east to west. Toward the 
southern and western portions of the heavens, all 
was clear starlight, Orion being particularly bril- 




liant ; the north was, as it were, overspread with 
a thin veil, through which the stars were barely 



visible. In the fourth change the northern lights 
resumed their three arches, but they were no 
longer concentric, the third being broken on the 
right into a portion of a fourth. Between the 
second and third there was the darkness of black- 
ness, while the third arch was light itself; but the 
lower arches were not so bright, and the lower 
nucleus was only darkish. 

The two following descriptions are from the pen 
of Professor Olmsted, of Yale College. They 
were given to the public immediately after the 
occurrence of the phenomena they respectively 
describe. The first took place on the 17th of 
November, 1835; the last on the 23d of April, 
1836. 

On the 17th of November, 1835, our northern 
hemisphere was adorned with a display of auroral 
lights remarkably grand and diversified. It was 
first observed at fifteen minutes before seven o'clock, 
when an illumination of the whole northern sky, 
resembling the break of day, was discernible 
through the openings in the clouds. About eigh- 
teen degrees east of north, was a broad column of 
shining vapor tinged with crimson, which appeared 
and disappeared at intervals. A westerly wind 
moved off the clouds, rendering the sky nearly 
clear by eight o'clock, when two broad, white col- 
umns, which had for some time been gathering be- 
tween the stars Aquila and Lyra on the west, and the 
Pleiades and Aries on the east, united above, so as 
to complete a luminous arch, spanning the heavens 
a little south of the prime vertical. The whole 
northern hemisphere, being more or less illuminated, 
and separated from the southern by this zone, was 
thrown into striking contrast with the latter, which 
appeared of a dark slate color, as though the stars 
were shining through a stratum of black clouds. 
The zone moved slowly to the south until about 
nine o'clock, when it had reached the bright star 
in the Eagle in the west, and extended a little south 
of the constellation Aries in the east. From this 
time it began to recede northward, at nearly a 
uniform rate, until twenty minutes before eleven, 
when a vast number of columns, white and crimson, 
began to shoot up, simultaneously, from all parts 



'gJgglTgJgBidMtlFa 



326 



WONDERS OF THE HEAVENS. 



of the northern hemisphere, directing their course 
towards a point a few degrees south and east of the 
zenith, around which they arranged themselves as 
around a common focus. The position of this point 
was between the Pleiades and Alpha Arietis, and 
south of the Bee. 

Soon after eleven o'clock, commenced a striking 
display of those undulatory flashes denominated 
merry dancers. They consisted of thin waves or 
sheets of light, coursing each other with immense 
speed. Those undulations which play upon the 
surface of a field of rye, when gently agitated by 
the wind, may give to the reader a faint idea of 
these auroral waves. One of these crimson columns, 
the most dense and beautiful of all, as it ascended 
towards the common focus crossed the planet 
Jupiter, then at an altitude of thirty-six degrees. 
The appearance was peculiarly interesting, as the 
planet shone through the crimson clouds with its 
splendor apparently augmented rather than di- 
minished. 

A few shooting stars were seen at intervals, some 
of which were above the ordinary magnitude and 
brightness. One that came from between the feet 
of the Great Bear, at eight minutes after one 
o'clock, and fell apparently near to the earth, 
exliibited a very white and dazzling light, and as 
it exploded, scattered shining fragments very much 
after the manner of a sky rocket. 

As early as seven o'clock, the magnetic needle 
began to show unusual agitation, and after that it 
was carefully observed. Near eleven o'clock, 
when the streamers were rising and the corona 
forming, the disturbance of the needle was very 
remarkable, causing a motion of one degree and 
five minutes in five minutes of time. This dis- 
turbance continued until ten o'clock the next 
morning, the needle having traversed an entire 
range of one degree and forty minutes, while its 
ordinary diurnal deflection is not more than four 
minutes. 

Another writer, speaking of the same appearance, 
says — We can compare the spectacle to nothing but 
an immense umbrella suspended from the heavens, 
the edges of which embraced more than half the 



visible horizon; in the south-east its lower edge 
covered the belt of Orion, and farther to the left the 
planet Jupiter shone in all its magnificence and 
glory, as through a transparency of gold and scar- 
let. The w^hole scene was indescribably beautiful 
and solemn. It was a spectacle of which painting 
and poetry united can give no adequate idea, and 
which philosophy will fail to account for to the 
satisfaction of the student of nature or the disciple 
of revelation. The cause can be known only to 
Him at whose bidding 

Darkness fled — Light shone, 
And the ethereal quintessence of heaven 
Flew upward, spirited with various forms 
That rolled orbicular, and turned to stars. 

The appearance of April 23d, 1836, is thus 
described by Olmsted : — Last night we were regaled 
with another exhibition of the auroral lights, in 
some respects even more remarkable than that of 
the 17th of November. It announced itself as early 
as a quarter before eight o'clock, by a peculiar kind 
of vapor overspreading the northern sky, resembling 
a thin fog, of the color of dull yellow, slightly 
tinged with red. From a bank of the auroral vapor 
that rose a few degrees above the northern horizon, 
a great number of those luminous columns called 
streamers ascended towards a common focus, situ- 
ated, as usual, a little south and east of the zenith, 
nearly or perhaps exactly at the magnetic pole of 
the dipping-needle. Faint undulations played on 
the surface of the streamers, affording sure prog- 
nostics of an unusual display of this mysterious 
phenomenon. The light of the moon, now near 
its first quarter, impaired the distinctness of the 
auroral lights, but the firmament throughout ex- 
hibited one of its finest aspects. The planet Venus 
was shining with great brilliancy in the west, 
followed at small intervals by Jupiter and the 
moon ; while the large constellations, Orion and 
Leo, with two stars of the first magnitude, Sirius 
and Procyon, added their attractions. The sky 
was cloudless, and the air perfectly still. 

There are but few examples on record of the 
auroral lights displaying themselves with peculiar 
magnificence in moonlight. 



WONDERS OF THE HEAVENS 



327 



Notwithstanding the presence of the moon, by 
half past ten o'clock, the auroral arches, streamers, 
and waves began to exhibit the most interesting 
appearances. No well-defined arch was formed, 
but broad zones of silvery whiteness, composing 
greater or less portions of arches, were seen in 
various parts of the heavens. Two that lay in the 
south, crossing the meridian at different altitudes, 
were especially observable. From each proceeded 
streamers, all directed towards the common focus. 
At the same time, those peculiar undulations called 
merry dancers were flowing in broad and silvery 
sheets towards that point, writhing around it in 
serpentine curves, and often assuming the most 
fantastic forms. The swiftness of their motions, 
which were generally upward, and often with their 
broadest side foremost, was truly astonishing. 
Toward the horizon the undulations were com- 
paratively feeble ; but from the elevation of about 
thirty degrees to the zenith, their movement was 
performed in a time not exceeding one second, — 
a velocity greater than we have ever noticed be- 
fore, which was still distinctly progressive. 

Five minutes after eleven o'clock, a few large 
streamers, of the whiteness of burnished silver, 
radiated from the common focus towards the east 
and the west. These were soon superseded by a 
mass of crimson vapor, rising simultaneously a little 
south of west and north of east, and ascending 
towards the focus in columns eight or ten degrees 
broad below, but tapering above. These disap- 
peared in about ten minutes, and the lights were 
subsequently a pure white, except an occasional 
tinge of red. During the appearance of the crim- 
son columns a rosy hue was reflected from white 
houses and other favorable surfaces, imparting to 
them an aspect peculiarly attractive. 

From this time until half past two o'clock, our 
attention was almost wholly absorbed in contem- 
plating the sublime movements of the auroral 
waves: they evidently were formations entirely 
distinct from the columns, which either remained 
stationary, or shot out a broad stream of white 
light towards the focus, while the waves apparently 
occupied a region far below them. 



At half past two o'clock, a covering of light 
clouds was spread over a large portion of the sky, 
and our observations were discontinued. At this 
time, although the moon was down, yet its absence 
produced little change in the general illumination; 
the landscape appeared still as if enlightened by the 
moon, and it was easy to discern the time of night 
by a watch, from the light of the aurora. 

The repeated occurrence of late of remarkable 
auroral exhibitions indicates that we are passing 
through one of those periods, which recur after long 
intervals, when this phenomenon presents itself with 
unusual frequency and magnificence. 



SECTION II. 

Remarkable halos and parhelia seen in France in April, 1666 — In 
March, 1667 — Huygens' explanation of the causes of such phenom- 
ena — Mariotte's explanation of halos— Mock-moon seen by Forster 
— Extraordinary circles round the moon seen at New Haven in 
November, 1827 — Phenomenon seen at Green Bay in February, 
1835 — Experiments illustrating the production of halos — Rain- 
bows — Experiments producing colored bows— Cause of rainbows — 
Remarkable bows observed by Brewster — At Chartres — By Halley 
—In 1710— In July, 1824— Clouds— Their modifications— Curl- 
cloud — S tacken-cloud — Fall-cloud — Sonder-cloud — Wane-cloud — 
Twain-cloud — Rain-cloud — Scud — The color of clouds — Their 
height — Their structure and buoyancy. 

On the ninth of April, 1666, about half past nine, 
A. M., there were observed (in France) three 
circles in the sky. One of them S C H N was very 
large, but little broken, and white everywhere 
without the least mixture of any other color. It 
passed through the middle of the sun's disc, and 
was parallel to the horizon. Its diameter was 
more than one hundred degrees, and its centre A 
near the zenith. The second circle D E B was 
much less, and deficient in some places, having the 
colors of the rainbow, particularly in the part 
within the greatest circle. It had the true sun for 
its centre. The third H D N was less than the 
first, but greater than the second ; it was not entire, 
but only an arch of a circle, whose centre was far 
distant from the sun, and whose circumference 
about its middle was near that of the least circle, 



328 



WONDERS OF THE HEAVENS. 



and intersected the greatest circle near its extremi- 
ties H, N. In this circle also were visible the 




colors of the rainbow, but not so strong as those 
of the second. There was a great brightness of 
the mixed prismatic colors at the point of nearest 
approach of this third and the smallest circle. At 
the points where the third circle intersected the 
largest there were two mock-suns or sun-dogs, 
H and N, which were very bright, yet not so 
bright or well defined as the true sun. Beside 
these two, there was on the circumference of the 
first great circle a third mock-sun C, situated to 
the north, which was less bright than the two first ; 
so that there appeared at the same time four suns 
in the heaven. There was also a very dark space 
bed between R and D. This phenomenon was 
considered very remarkable, both because of the 
eccentricity of the circle H D N, and the situation 
of the parhelia or false suns, they not being at the 
intersection of the circle D E B with the great 
circle S C H N, but in that of the semicircle H D 
N. These are different from the position of the five 
suns seen at Rome in March, 1629, — two of them 
appearing in the intersection of a circle passing 
through the sun's disc with another that was con- 
centric with the sun. 

A circle round the sun was seen at Paris on 



March 12th, 1667, about nine in the morning, 
the diameter of which was forty-four degrees, 
and the breadth of its limb about half a degree. 
The upper and lower parts were of a vivid red and 
yellow with a little purple, but especially the upper. 
The other parts appeared whitish and of little clear- 
ness. The space within the circle was rather 
darker than that around it, especially toward the 
parts that were colored. Besides this circle there 
was a portion of another and larger circle, which 
touched the first, with its extremities bent down- 
ward. This portion had its colors also, but they 
were fainter than those of the whole circle. There 
were small clouds in the air, that somewhat tar- 
nished the blue of the sky, and lessened the bright- 
ness of the sun, which seemed as if it were eclipsed. 
This circle or halo appeared in the same beauty 
and splendor till about half after ten, when it 
began to fade gradually, continuing visible till two 
in the afternoon. Huygens, who was with a large 
company observing the phenomena, made known 
his theory concerning the cause, not only of the 
halos, but of the parhelia, which had before been 
considered as prodigies, and forerunners of some 
singular event. As to the halos, they were formed 
by small round grains, made up of two parts, one 
transparent and the other opaque, the latter being 




enclosed in the former as the stone in the cherry ; 
as may be seen in the figure, where A A represents 



WONDERS OF THE HEAVENS 



329 



one of these grains, and B the opaque part. He 
explained how some of these little grains (that 
swim up and down in the air between us and the 
sun, being less distant from the axis which ex- 
tends from the sun to the eye than a certain angle) 
necessarily hinder the rays that fall on them from 
reaching our eyes, since the opaque part will cause 
behind every such grain a space of a conical figure, 
as M N 0, in which the eye of the spectator being 
situated, cannot see the sun through that grain, 
though it may see it when situated elsewhere, as at 
P. The effect of these grains suspended in the air 
may be better comprehended by reference to the 
next figure ; in which B is the place of the eye ; 




B A the axis drawn from the eye to the sun; 

C, M, F some of the grains, with their kernels 

making them semi-opaque. Among these the 

grain C, being in the axis B A, (the lines C K, 

L H representing the rays of the sun nearest to 

the axis, the passage of which is not prevented 

by the opacity of the kernel,) will not be able to 

transmit any ray of the sun to B ; and if we conceive 

a cone having its vertex at the eye and its sides 

B D, B E parallel to the rays C K, L H, all the 

grains M, M, &c. which this cone may comprise 
42 



will not suffer any ray to pass to the eye, because 
the eye must be in the cone of their obscurity ; but 
those grains that are without this cone, as at 
F, F, &c. will let the rays pass, because the eye is 
out of the cone of their obscurity ; whence it follovv^s, 
that the angle of this cone D B E determines the 
diameter of the halo, which depends on the propor- 
tion of the opaque to the transparent part of the 
grain. If this diameter be forty-four degrees, the 
size of the opaque grain will be to that of the trans- 
parent as forty to nineteen. But the proportion 
varies in different grains of the same assemblage, 
consequently we sometimes see several halos, one 
around the other, all having their centre at the sun. 
The halos are sometimes colored, for the same 
reason that the spectrum formed by a triangular 
prism is colored. The space within the halo, and 
particularly that near the parts most vividly colored, 
appears obscurer than the space without, because 
there those grains are the most numerous which 
transmit no rays of the sun to the eye, and only 
darken the air, like drops of water when it rains. 

As to the arch which touched the halo above- 
mentioned, (seen at Paris on the 12th of March,) 
and as to the greatest brightness being at the point 
of contact and at the point opposite, these effects 
did not proceed from the grains before spoken of, 
but from another cause, which also produced the 
mock-suns. On this subject Huygens remarked 
that, beside the round and semi-opaque grains, 
there were also formed in the air certain little 
cylinders. These — being such as are represented 
in the annexed figure, oblong, and rounding at both 



\ 





ends, with an inner kernel of the same shape — from 
their different arrangement would produce all the 
appearances of the mock-suns and their circles. 

Some of these cylinders being erect, there must 
appear in the heavens a large white circle parallel 



330 



WONDERS OF THE HEAVENS 



to the horizon, passing through the sun, and of 
nearly the same breadth as that luminary; as was 
observed in the phenomenon seen at Rome in 1629, 
of which Gassendus and Descartes have written, 
and of which the following figure is a representa- 
tion. The circle L K N M is caused by the reflec- 
tion of the rays of the sun on the surface of the 
cylinders, there being none that can reflect his 
rays to our eyes except those which are elevated 
above the horizon at the same angle as the sun ; 




whence it follows that the circle must appear 
white, of equal altitude with the sun, and conse- 
quently parallel to the horizon. Considering the 
transparency of these perpendicular cylinders and 
their opaque kernels, it is easily seen that those of 
the white circle which are distant from the sun at 
a certain angle begin to give passage to such rays 
as reach our eyes, in the manner already stated 
respecting the round, half dark grains. These are 
the cylinders that, on each side of the sun, cause 
us to see a parhelion in the large white circle, as 
in the figure above, where they are marked K 
and N. These parhelia have commonly luminous 
tails, because the cylinders following those that 
form the parhelia, and which are yet farther distant 
from the sun, also let the rays pass to our eyes ; so 
that these tails may be more than twenty degees 
in length. The same parhelia are colored, because 
they are made, like the halo, by refraction. There 



are two other images of the sun caused by these 
perpendicular cylinders, and so situated in the 
large white circle, that the spectator turning his 
face toward the true sun has them behind him; 
as the parhelia at L and M in the last figure. 
These are produced by two refractions and one 
reflection in the cylinders, in the same manner as 
the common rainbow in the drops of rain ; so that 
the opaque kernels do nothing toward the produc- 
tion of these two suns, but sometimes even prevent 
their appearance. 

These two parhelia are more or less near each 
other, according to the greater or less altitude of 
the sun. They are colored, but when faint they 
may seem white, as the halos do when they are not 
very bright. The same perpendicular cylinders 
can also produce a halo by the rounding of their 
ends, so that when distant from the sun at a 
certain angle, they begin from that position to give 
passage to the rays, transmitting them to the 
spectator. The halos thus formed are probably 
those that pass through the two parhelia which 
are at the side of the true sun, as GKNI in the 
last figure. 

There is yet another situation of these cylinders, 
such that their axes are parallel to the horizon, 
yet turned various ways, like needles thrown on 
the ground confusedly. It is in these cylinders 
that the arches are formed which touch the halos 
above or below. The figure of these arches is 
different, according to the different altitudes of the 
sun. When the sun is very near the horizon, such 
an arch, appearing on an ordinary halo of forty-four 
degrees, must show like two horns ; but the sun 
rising higher, those horns become lower in propor- 
tion. The reason why these arches usually touch 
a parhelion is, that the same horizontal cylinders 
which produce the arch, produce also that parhe- 
lion by means of their two round and transparent 
ends, in the same manner as has been said of the 
perpendicular cylinders. In these same cylinders 
parallel to the horizon, there is also found the 
cause of the white cross observed with the para- 
selene or mock-moons by Hevelius, the perpen- 
dicular fillet of that cross coming from the reflection 



WONDERS OF THE HEAVENS 



331 



of the moon on the surface of these cylinders, as 
the other fillet, parallel to the horizon, is produced 
by the reflection of the perpendicular cylinders 
that make the great white circle of which this 
fillet is a part. To produce this effect the moon 
must not be very high. 

Besides the perpendicular and the parallel 
cylinders, there are often a great many that move 
to and fro in the air in all sorts of positions ; these 
will produce a halo round the sun, and even a 
more vivid one than that caused by the grains, in- 
asmuch as each cylinder sends many more rays to 
the eye than each of these little spheres. The 
little halo D E F in the Roman phenomenon may 
well have been caused by such cylinders. 

As to those mock-suns which sometimes show 
themselves directly opposite the true sun, Huygens 
could find nothing that should make these suns 
necessarily meet in the great white circle parallel 
to the horizon. For the production of those suns 
he supposed a number of small cylinders with 
opaque kernels, like the foregoing, which were 
carried in the air neither perpendicularly, nor 
horizontally, but inclined to the plane of the 
horizon at a certain angle, (being nearly ninety 
degrees;) among which are to be numbered those 
cylinders which Descartes saw fall from the 
heavens having stars at both ends, such as are 
here shown. In these cylinders was found not 




only the cause of the anthelia made by the inter- 
section of two arches, as in the next figure, but 
also that of some other extraordinary arches and 
rods that are sometimes observed near the sun. 

To make all these different effects of the cylin- 
ders manifest to the eye, Huygens produced one 
of glass, a foot long, of the shape first figured in 
this section; and for the opaque kernel in the 



middle, a cylinder of w^ood, the intermediate space 
being filled with water instead of transparent ice. 




This cylinder being exposed to the sun, and the eye 
properly stationed, there were successively seen all 
the reflections and refractions above-rnentioned. 

Mariotte finds a cause for halos in the form of 
those small, transparent, prismatic needles of which 
snow is composed. In congealing, water assumes 
very regular crystalline shapes, among which we 
often meet with those whose faces make angles of 
sixty degrees, thus constituting prisms of ice whose 
refracting angle is sixty degrees. These prisms, 
being turned in the air all possible ways, will 
receive the solar rays under all possible inclina- 
tions. But in certain positions of the prisms, light 
passing through them experiences the least possible 
deviation: this position is such that the refracted 
ray makes an isosceles triangle with the two sides 
of the prism, or that the angle of refraction is 
equal to half the refracting angle. As the re- 
fracting angle is here sixty degrees, the angle of 
refraction will be thirty degrees, and the angle of 
incidence about forty-one degrees. In this case, 
the angle of deviation is equal to twice the angle 
of incidence diminished by the refracting angle, 
which gives twenty-two degrees nearly for half the 
diameter of the halo. 



332 



WONDERS OF THE HEAVENS 



then imagine, (the observer being 
situated at P,) that when the direct rays ^'■ 



We may 
situated at jl ,) tuat »vj 
the direction SP, all 



=11 liic uiiov^t iaj3 arrive in 
the small prisms of sixty 




degrees floating in the higher regions of the atmo- 
sphere, and turned like the prism A C B, will 
reflect toward the eye a small, but very bright 
beam, because, this will be composed of rays 
sensibly parallel; and the same phenomenon re- 
producing itself in a conical surface, and making 
an angle of twenty-two degrees about the line S P 
drawn to the sun's centre, a crown of forty-four 
degrees in diameter will be visible. The refrac- 
tion of the violet ray being greater than the red, 
we shall have for this ray a greater crown. The 
sun's diameter, being thirty minutes, will increase 
the breadth of the colored bands. 

Dr. Forster, in a paper read before the Meteo- 
rological Society of London, and published at the 
time, mentions a curious lunar refraction which he 
observed some years before. About seven o'clock 
in the evening, the moon being five days old, he 




noticed a double refraction of the above form and 
relative position; that is, two distinct crescents 



instead of one, and so precisely similar that it 
could not be distinguished which was the parase- 
lene or mock-moon, and which the true. Forster 
thought this phenomenon analogous to the double 
refraction in certain laminated spars, and that it 
might have indicated the existence of atmospherical 
laminae at that time, such a condition of the atmo- 
sphere being perhaps connected with the various 
counter currents of the air which are known to 
exist at the same time at different altitudes. 

Singular Appearance of Circles round the 
Moon. On the evening of the 2d of November, 
1827, between the hours of seven and eight, there 
appeared around the moon (a little more than its 
width in diameter) a very luminous saffron-colored 
light. On the outer edge was a circle of bright 




red, which was surrounded by a dark purple; 
around the purple was a circle of bright blue, 
which faded into a yellowish green, increasing 
toward the outer edge to a very vivid green. 
There appeared to be faint white rays passing from 
the moon across these columns, whose circles 
formed, around this lunar glory, a larger circle of 
a dark leaden color, which gave the whole a very 
beautiful appearance. This was observed by a 
great number of spectators at New Haven, who all 
said that they had never seen any thing of the kind 



WONDERS OF THE HEAVENS. 



333 



equal to it in the course of their lives; and some 
of these Spectators were aged people. A young 
lady copied the hues at the moment, and before 
they had changed or materially faded. The plate 
is a very correct representation of the appearance 
as it was seen by the editor of the American 
Journal of Science, from which the plate and 
account were taken. 

At Fort Howard, Green Bay, Michigan, there 
was observed, on the 27th of February, 1835, a 
large and brilliant halo round the sun, with two 
parhelia, A and B, within the circumference at the 
extremities of its horizontal diameter, but little 
inferior in brilliancy to the true sun; they were 
accompanied by luminous trains opposite the true 
sun. Immediately above and beneath the sun in 




the circumference of the same circle, at E and F, 
there were bright luminous spots of an elliptical 
form, less intense in brilliancy than the first, but 
much larger; from the highest point, rays faintly 
colored and slightly curved appeared to emanate, 
forming a small arc of a greater circle than the 
halo. Another circle, the plane of which was 
horizontal, at right angles to and of greater diam- 
eter than the first, with its centre apparently in 
the zenith, completely surrounded the heavens; 
its circumference passed through the sun and the 
mock-suns A and B, and these last were distinctly 
reflected in the opposite part of the heavens at 
C and D. Between the zenith and the sun were 
two faintly luminous arcs, convex toward and nearly 
tangent to each other. These are not represented 
in the cut. Two well-defined and quite brilliant 



rainbows, G and H, situated on the right and left 
of the halos, and with their convexity toward 
the mock-suns, completed this interesting appear- 
ance. 

This phenomenon was first observed a little 
before eight o'clock in the morning, the lower part 
of the halo being then about two degrees above 
the horizon, its diameter descending as the sun 
ascended. It was most brilliant and splendid at 
fifteen minutes before ten, when it began to fade, 
and finally disappeared about fifteen minutes before 
eleven, the total duration having been about three 
hours. 

The production of halos may be illustrated ex- 
perimentally by crystallizing various salts upon 
plates of glass, and looking through the plates at 
the sun or a candle. When the crystals are 
granular and properly formed, they will produce 
the finest effects. A few drops of a saturated 
solution of alum, for example, spread over a plate 
of glass so as to crystallize quickly, will cover it 
with an imperfect crust, consisting of flat, octahe- 
dral crystals, scarcely visible to the eye. When 
the observer, with his eye placed close behind the 
smooth side of the glass plate, looks through it at 
a luminous body, he will perceive three fine halos, at 
different distances, encircling the source of light. 
The interior halo, which is the whitest of the three, 
is formed by the refraction of the rays through the 
crystals that are least inclined to each other. The 
second halo, which is blue without and red within, 
with all the prismatic colors, is formed by a pair 
of more inclined faces ; and the third halo, which 
is large and brilliantly colored, from the increased 
refraction and dispersion, is formed by the most 
inclined faces. As each crystal has three pairs 
of each of these included prisms, and as these 
refracting faces will have every possible direction 
to the horizon, it may be understood how the halos 
are completed and equally luminous throughout. 
When the crystals have the property of double 
refraction, and when their axis is perpendicular to 
the plates, more beautiful combinations will be 
produced. 



334 



WONDERS OF THE HEAVENS 



THE RAINBOW. 

This, as every one knows, is a luminous arch 
extending usually across the region of the sky 
opposite the sun. Under favorable circumstances, 
two bows are seen, the inner and the outer, or 
the primary and the secondary. Within the primary, 
in contact with it, and without the secondary, 
there have been seen supernumerary bows. The 
primary, or inner bow, which is commonly seen 
alone, is a part of a circle whose radius is forty- 
two degrees. It consists of seven differently 
colored bows, viz. violet, which is the innermost, 
indigo, blue, green, yellow, orange, and red, which is 
the outermost. These colors have the same pro- 
portional breadth as the spaces in the prismatic 
spectrum. This bow is, therefore, only an infinite 
number of prismatic spectra, arrayed in the cir- 
cumference of a circle ; and it would be easy by a 
circular arrangement of prisms, or by covering up 
all the central part of a large lens, to produce a 
small arch of exactly the same colors. All that 
we require, therefore, to form a rainbow, is a great 
number of transparent bodies capable of forming a 
great number of prismatic spectra from the light of 
the sun. 

As the rainbow is never seen unless when rain 
is actually falling between the spectator and the 
sky opposite to the sun, we are led to conclude 
that the transparent bodies required are drops of 
rain, which we know to be small spheres. If we 
look into a globe of glass, or water, held above 
the head and opposite to the sun, we shall actually 
see a prismatic spectrum reflected from the farther 
side of the globe. In this spectrum the violet ray 
will be innermost, and the spectrum Avill be verti- 
cal. If we hold the globe horizontal on a level 
with the eye, so as to see the sun's light reflected 
in a horizontal plane, we shall see a horizontal 
spectrum with the violet ray innermost. If we 
hold a globe in a position intermediate between 
these two, so as to see the sun's light reflected in 
a plane inclined forty-five degrees to the horizon, 
we shall perceive a spectrum inclined forty-five 
degrees to the horizon, with the violet ray inner- 
most. Since, in a shower of rain, there are drops 



in all positions relative to the eye, the eye will 
receive spectra inclined at all angles to the horizon, 
so that when combined they will form the large 
circular spectrum which constitutes the rainbow. 
To explain this more clearly, let E, F be drops of 




rain exposed to the sun's rays, incident upon them 
in the direction RE, R F ; out of the whole beam 
of light which falls upon the drop, those rays which 
pass through or near the axis of the drop will be 
refracted to a focus behind it ; but those which fall 
on the upper side of the drop will be refi^acted, the 
red rays least, and the violet most, and will fall 
upon the back of the drop with such an obliquity 
that many of them will be reflected. These rays 
will be again refracted, and will meet the eye at 0, 
which will perceive a spectrum, or prismatic image 
of the sun, with the red space uppermost and the 
violet undermost. If the sun, the eye, and the 
drops E, F are all in the same vertical plane, the 
spectrum produced by E, F will form the colors at 
the very summit of the bow. Let us suppose a 
drop to be near the horizon, so that the eye, the 
drop, and the sun are in a plane inclined to the 
horizon ; a ray of the sun's light will be reflected 
in the same manner as at E, F, with this difference 
only, that the plane of reflection will be inclined to 
the horizon, and will form part of the bow distant 
from the summit. Hence it is manifest that the 
drops of rain above the line joining the eye and the 
upper part of the rainbow, and in the plane passing 



WONDERS OF THE HEAVENS 



335 



through the eye and the sun, will form the upper 
part of the bow; and the drops to the right and 
left of the observer, and without the line joining the 
eye and the lowest part of the bow, will form the 
lowest part of the bow on each hand. Not a single 
drop, therefore, between the eye and the space 
within the bow is concerned in its production; 
so that if a shower were to fall regularly from a 
cloud, the rainbow would appear before a single 
drop of rain had reached the ground. 

If we compute the inclination of the red ray and 
the violet ray to the incident rays RE, R F, we 
shall find it to be forty-two degrees and two 
minutes for the red, and forty degrees and seven- 
teen minutes for the violet, so that the breadth of 
the bow will be the difference of those numbers, or 
one degree and forty-five minutes — nearly three 
times and a half the sun's diameter. These results 
coincide so accurately with observation as to leave 
no doubt that the primary rainbow is produced by 
two refractions and one intermediate reflection of 
the rays that fall on the upper sides of the drops 
of rain. The red and violet rays will suflfer a 
second reflection at the points where they are 
represented as quitting the drop, but these reflect- 
ed rays will go upward, and cannot possibly reach 
the eye at 0. But though this is the case with 
rays that enter the upper side of the drop as at 
E F, or the side farthest from the eye, yet those 
which enter it on the under side, or the side nearest 
the eye, may, after two reflections, reach the eye 
as shown in the drops H, G, where the rays R, R 
enter the drops below. The red and violet rays 
will be refracted in different directions, and after 
being twice reflected, will be finally refracted to 
the eye at 0, the violet forming the upper, the red 
the under part of the spectrum. If we compute 
the inclination of these rays to the incident rays 
R, R, we shall find them to be fifty degrees and 
fifty-seven minutes for the red, and fifty-four degrees 
and seven minutes for the violet ray ; the difference 
of which, three degrees and ten minutes, will be 
the breadth of the bow, and the distance between 
the bows will be eight degrees and fifty-five min- 
utes. Hence it is clear that a secondary bow will 



be formed exterior to the primary, and with its 
colors reversed, in consequence of their being 
produced by two reflections and two refractions. 
The breadth of the secondary bow is nearly twice 
as great as that of the primary, but its colors must 
be much fainter, because it consists of light that 
has suffered two reflections. 

Newton found the semidiameter of the interior 
bow to be forty-two degrees, its breadth two de- 
grees and ten minutes, and its distance from the 
outer bow eight and a half degrees — numbers 
which agree so well with the calculated results as 
to leave no doubt of the truth of the explanation 
given above.* The production of artificial bows 
by the spray of a water-fall, or by the drops scat- 
tered from a wet cloth or forced out of a syringe, 
is another proof of the correctness of the explana- 
tion. Lunar bows, and many peculiar solar bows, 
have been seen and described. 

On the 5th of July, 1828, Brewster observed 
three supernumerary bows within the primary, 
each consisting of green and red arches, and in 
contact with the violet arch of the primary bow. 
On the outside of the secondary bow there was a 
red arch, and beyond it a very faint green one, con- 
stituting a supernumerary bow analogous to those 
within the primary. 

Two extraordinary rainbows were seen at Char- 
tres on the 10th of August, 1665, about half an 
hour past six in the evening, crossing each other 
nearly at right angles as seen in the figure. That 
opposite the sun in the usual manner was more 
deeply colored than that which crossed it, though 
the colors of the first were not indeed so strong as 
they are seen at other times. The greatest height 
of the strongest rainbow was about forty-five de- 
grees ; the feebler bow lost one of its legs, growing 
fainter above the stronger bow, but the leg below 
appeared continued to the horizon. The fainter 
seemed a portion of a great circle; but the stronger, 
as usual, a portion of a small circle. The sun at 

* If any farther evidence were wanted, it might be found in a fact 
observed in 1812 by Brewster, viz. that the light of both the bows is 
wholly polarized in planes passing through the eye and the radii of 
the arch. 



336 



WONDERS OF THE HEAVENS 



their appearance was about six degrees above the 
horizon, and the river of Chartres, which runs 




south, was between the observer and the bows; 
he stood level with the river, one hundred and 
fifty paces from it. 

On the 6th of August, 1698, Dr. Halley observed 
a remarkable rainbow, shown in the succeeding 
figure,, where A B C is the primary bow, D H E the 




secondary, and A F H G C the new bow intersect- 
ing the secondary D H E, and dividing it nearly 
into three parts. Halley observed the points F, G 
to rise, and the arch F G gradually to contract, till 
at length the two arches F H G and F G coincided, 
so that the secondary iris for a great space lost its 
colors, and appeared like a Avhite arch at the top. 
The new bow A H C had its colors in the same 
order as the primary ABC, and therefore the two 
spectra at G F counteracted each other and pro- 
duced the white arch. The sun at this time shone 
on the river Dee, which was unruffled, and Halley 
found that the bow A H C was only that part of 
the circle of the primary that would have been 



under the castle, bent upward by reflection from 
the river. 

On Christmas day in the year 1710, a gentleman, 
walking about eight o'clock in the evening, "to 
his great delight saw a bow that the moon had 
fixed in the clouds." The moon was at the time 
nearly full ; the evening had been rainy, but the 
clouds had broken and the moon shone pretty 
clear. This iris had all the colors of a solar bow 
exceedingly distinct and beautiful, though dimmer 
than those we see by day. It continued about ten 
minutes, when the interposition of clouds hindered 
farther observation. Dr. Piatt, of Oxford, England, 
observed a similar phenomenon at that town on the 
23d of November, 1675. 

The following is from a journal kept on board a 
ship in the Pacific Ocean, July 13th, 1824. "This 
afternoon we were gratified with an unusual and 
beautiful sight, viz. part of four distinct, concentric 
rainbows all united to each other. The principal 
or outer bow made the usual angle with the sun, 
and was the broadest; the others diminished in 
size and brightness, but the prismatic colors were 
distinctly seen in each, and were all in the same 
order. The secondary bow, often seen at a dis- 
tance from the primary with colors reversed, was 
not seen. The bow was complete to the horizon, 
but the compound part was not above twenty de- 
grees in length; this part did not appear to be 
broader than that which was single. The sun 
was about twelve degrees above the western 
horizon, shining through the interstices of a very 
dense broken cloud, each aperture appearing 
almost as bright as the sun itself. This was 
considered by the observer as the cause of the 
phenomenon. 

CLOUDS. 

The presence of the ocean of vapor which is 
constantly ascending from the earth and consti- 
tuting part of the atmosphere is not always evi- 
dent to the sight; in its elastic state it is invisible, 
and therefore it is only in some of its changes 
that the eye can detect it. By one of the most 
remarkable of these, those masses of visible aqueous 



WONDERS OF THE HEAVENS. 



337 



vapor are formed, which, floating in the sky, or 
drifting through it with the wind, at different 
elevations, with every variety of color and form, 
are called clouds; or which, recumbent on the 
surface of the land or of the water, and spread 
over greater or smaller portions of them, are de- 
nominated /ogs, or mists, according to their intensity. 
In all cases their composition is similar, and con- 
sists of the moisture deposited by a body of air in 
minute globules. 

Their formation, in every position, is a conse- 
quence of decrease of temperature in some parts 
of the atmosphere where a certain proportion of 
aqueous elastic vapor is present; but in those 
where the latter condition may be wanting, it is 
evident that the development of clouds will not 
follow the decrement of temperature. Nothing is 
more common than the fact of the necessary condi- 
tions existing in some of the atmospheric strata, 
and at the same time being absent in others ; and 
thus we can understand the causes of the alternate 
beds of clouds and clear air which often diversify 
the sky in serene weather. We can hence also 
comprehend how, in stormy weather, a solitary 
cloud sometimes appears to be stationary over a 
mountain-top, while myriads of other clouds drift 
past it on the gale. An observer on the summit 
feels the dew-drops of the seemingly fixed cloud 
sweeping by with great velocity, and discovers the 
stationary aspect which it exhibited below to be 
altogether an illusion. The fact is, the inferior in- 
visible beds of air are relatively warmer and more 
moist; they dash against the sloping side of the 
mountain, and are reflected up to the plane of con- 
densation in the atmosphere, where they give out 
their excess of water in the form of clouds. Above 
the cooling influence of the mountain-top the tem- 
perature of the air may not be depressed to the 
same point, and hence it continues clear. 

If the globules of water which constitute a cloud 
descend in consequence of their weight, and come 
once more within the influence of an elevated 
temperature, the aqueous vapor necessarily be- 
comes again invisible. In this way the under 

surface of a stratum of clouds becomes nearly 
43 



parallel, or rather concentric, with the surface of 
the sub-adjacent landscape over which it floats. 
Above this first range of clouds the temperature 
may still be considerably higher, and hence another 
large body of air must be passed through before a 
temperature sufficiently low be arrived at to cause 
a second deposition of clouds. 

Fresnel ingeniously supposes that the air con- 
tained between the minute globules of vapor, or 
the very fine crystals of snow which form a mass 
of clouds, is always of a higher temperature than 
the surrounding clear air. He supports this opinion 
on the well-known facts that the rays of the sun 
will pass through the air without heating it, unless 
the air be in contact with water, land, or some 
other reflecting object. The cloud accordingly 
forms such a body as will stop the sun's rays, and 
force them to warm, not only the air in external 
contact with it, but all the air in its interstices. It 
follows, therefore, that though the mass of waters 
in a cloud be heavier than the surrounding air, the 
warmer air in the interior of the cloud buoys it up 
and causes it to float. 

Gay-Lussac, on the other hand, refers the 
mounting of clouds in the air to the impulsion of 
the ascending currents which result from the dif- 
ference of temperature between the surface of the 
earth and the air in elevated regions. 

The formation of clouds may be observed with 
most advantage in Alpine countries, as they are 
there so frequently produced under the eye, upon 
the sides or the summits of mountains, by the con- 
densation of the vapor in the sheet of air immedi- 
ately over them. A mountain cloud is at first of 
but small extent, but it enlarges insensibly, and is 
swept by the winds into the bosom of the air, where 
it either meets and unites with others, or various 
tufts of these are scattered over the sky. These 
aerial groups appear, while drifting through the 
sky, to avoid dashing themselves upon the moun- 
tain peaks in their course ; and, as if endowed with 
instinctive repulsion, they bound over the crest of 
a mountain in a concentric curve, and slide down 
into the valley on the other side. The French 
naturalists, with much plausibility, ascribe this 



338 



WONDERS OF THE HEAVENS 



beautiful phenomenon to electricity. Bory de St. 
Vincent thinks, that, when small tufts of cloud are 
carried towards the sides or the summit of a moun- 
tain, they move with less rapidity than the force 
(wind) which moves them, and this force conse- 
quently arriving sooner at the obstacle, is reflected, 
and meets and checks the cloud in its progress. 

Clouds are distinguished into seven modifications, 
the peculiarities of which seem to be caused by the 
agency of electricity ; for example, three primary 
modifications, the Cirrus or Curl-cloud, the Cumu- 
lus or Stacken-cloud, and the Stratus or Fall- 
cloud; two Avhich may be considered intermediate 
in their nature, the Cirrocumulus or Sonder-cloud, 
and the Cirrostratus or Wane-cloud ; one which 
appears to be a compound, the Cumulostratus or 
Twain-cloud ; and lastly the Nimbus or Rain-cloud, 
a state which immediately precedes and attends 
the resolution of clouds into water. 

By this classification and nomenclature their ap- 
pearances may be noted down and transmitted to 



contemporary and future observers, for the purposes 
of comparison and record. A great advance has 
consequently been made in the perspicuous descrip- 
tion which has succeeded to the vague and unintel- 
ligible generalities of preceding ages. 

In the engravings are representations of the 
more usual forms of these genera, and a few 
remarks on each are subjoined to render their 
classification still more easy. 

CuRL-cLouD. The curling and flexuous forms of 
this cloud constitute its most obvious external 
character, and from these it derives its name. It 
may be distinguished from all others by the light- 
ness of its appearance, its fibrous texture, and the 
great and perpetually changing variety of figures 
which it presents to the eye. It is generally the 
most elevated, occupying the highest regions of 
the atmosphere. 

The comoid curl-cloud, vulgarly called the mare's 
tail, is the proper cirrus. It has, as represented 
in the engraving, figure first, somewhat the appear- 




ance of a distended lock of white hair, or of a 
bunch of wool pulled out into fine, pointed ends. 

In variable and warm weather in summer, when 
there are light breezes, long and obliquely de- 
scending bands of cirrus are often observed, and 
seem sometimes to unite distinct masses of clouds 
together. Frequently, by means of the interposi- 
tion of these curl-clouds between a stacken-cloud 
and some other cloud, (as, for example, the wane- 
cloud,) the twain-cloud, and ultimately the rain- 
cloud, is formed. 



Upon a minute examination of the cirrus, every 
particle is found to be in motion, while the whole 
mass scarcely changes its place. Sometimes the 
fibres which compose it gently wave backwards 
and forwards to and from each other. 

After a continuance of clear, fine weather, the 
cirrus is often observed as a fine, whitish line of 
cloud, at a great elevation, like a white thread 
stretched across the sky, the ends of which seem 
lost in each horizon. 

To this line of cirrus others are frequently added 



WONDERS OF THE HEAVENS 



339 



laterally, and sometimes, becoming denser by de- 
grees and descending lower in the atmosphere, 
inosculate* with others from below and produce 
rain. To this kind the name of linear cirrus 
(figure fifth) has been given. Sometimes, on the 
sides of the first line of a cirrus, clouds of the same 
kind are propagated, and sent off in an oblique 
or transverse direction, so that the whole phenom- 
enon has the appearance of net- work; this has 
been denominated reticular cirrus. 

Figure second represents a cirrus lengthened 
out to a long, pointed tail ; figure third a cirrus 
beginning to change to a cirrocumulus or sonder- 
cloud ; figure fourth a variety figured like the cyma 
of architecture. 

Though the above-mentioned varieties of the 
cirrus are all composed of straight lines of cloud, 
either parallel, or crossing each other in different 
directions, they are ranged under the head of czVrMs, 
or curl-cloud, from their analogy of texture to the 
substance from which this cloud is named. 

The cirrus is a cloud that appears to have the 
least density, the greatest variety of* extent and 
direction, and generally the most elevation. It 
may well be called the Proteus of the sky; for 
in some kinds of weather its figure is so rapidly 
changed, that after turning the eye away for a 
few moments, it may be found so completely 
altered as scarcely to be identified. But this is 
not the case universally, for it sometimes remains 
visible hours, and even days, with very little 
change. That the varieties are the effect of a 
variation in the cause of the clouds, cannot be 
doubted; many of them are attendant upon partic- 
ular kinds of weather. When the weather is dry 
the curl-cloud has more of a fibrous texture than 
when it is damp ; and whatever may be its figure, 
its extremities are always fine points, probably for 
the easier transmission of the electric fluid. These 
points are consequently directed toward that part 
of the sky with which the electric communication 
is to take place. 

In wet weather this cloud, being seen in the 
intervals of the rain, is ill defined, and often of a 

* Inosculation is a union by the conjunction of the extremities. 



sort of plumose figure, (i. e. giving the idea of the 
folded ends of a plume,) and has less of the fibrous 
structure ; this may be caused by its being sur- 
rounded with moister air, which is a conductor, 
though an imperfect one. There is, therefore, not 
the same necessity for the cloud's extension into 
fine points, as the fluid can fly off" from all parts of 
it. The plumose cirrus often appears when the 
sky is deep blue, and that of fibrous structure when 
the sky is pale-colored. But the intensity of the 
blue of the sky does not seem to depend on the 
dryness of the air ; indeed. Sir Isaac Newton re- 
marked that the deepest blue happened just at the 
change from a dry to a moist atmosphere. 

The detached cirri called mares' tails are seldom 
very much elevated ; their presence is well known 
to be an indication of wind, and when their termi- 
nations have a decided direction, the wind that 
ensues has been often found to blow from the quar- 
ter to which they have pointed. This circumstance 
cannot well be explained. 

There is sometimes a kind of motion observable 
in the cirri which is difficult to describe, and which 
seems only to take place in that variety that has 
a plumose extremity, with a long, fibrous body and 
a fine, pointed tail. The plumose head (which is 
clear and more fibrous than usual) and the body 
seem in motion, as if every particle were alive. 
Can this motion be the effect of an effort on the 
part of the electrified particles of the cloud to 
equalize their own electricity with that of the air? 
or is there some disturbance in the electricity 
within the cloud, from other causes? or can the 
motion be occasioned by the evolution of air gene- 
rated in the cloud? 

When the curl-cloud ceases to conduct, it changes 
its form and becomes some other cloud; thus 
sometimes a sky-full of cirrous streaks after a 
while become overspread with a milky whiteness. 
This is a sort of change to a wane-cloud, which 
often ends in rain. The curl-clouds, however, 
frequently change to the sonder-cloud, and in 
the progress of the change the fibres seem to 
shoot out laterally into transverse and intersecting 
streaks. They change first at their points of inter- 



l^i^ 



340 



WONDERS OF THE HEAVENS 



section, which thicken, approach to the orbicular 
form, and seem like centres, from which fibres 
irradiate ; thus a sort of stelliform sonder-cloud is 
formed, which either goes on changing into a more 
perfect feature of that cloud, or changes again to 
curl-cloud or to wane-cloud, or evaporates. 

Stacken-cloud. This cloud is easily known by 
its irregular hemispherical or heaped superstruc- 
ture ; hence its name cumulus, a heap or pile. It has 



usually a flattened base. The mode of its forma- 
tion is by the gathering together of detached 
clouds, which then appear stacked into one large 
and elevated mass, or stacken-cloud. The best 
time for viewing its progressive formation is in fine, 
settled weather. About sunrise, small, thinly-scat- 
tered specks of clouds may be observed. As the 
sun rises these enlarge, those near each other 
coalesce, and at length the cumulus is completed. 




It maybe called the cloud of day, as it usually exists 
only during that period, dissolving in the evening, 
in a manner the exact counterpart of its formation 
in the morning. Those stacken-clouds which are 
of a more regular hemispherical form, whitish- 
colored, and which reflect a strong silvery light 
when opposed to the sun, appear to be connected 
with electrical phenomena. Those seen in the 
intervals of showers are more variable in form, 
and more fleecy, with irregular protuberances. 
When this kind of cloud increases so as to obscure 
the sky, its parts generally inosculate, and begin to 
assume that density of appearance which charac- 
terizes the twain-cloud. 

Some of the little stacken-clouds are not so fleecy 
as the rest ; they are more compact in form, and 
flying along rapidly between the showers, are 
considered as a foreboding of their return, and are 
hence by some called water-wagons. 

It is curious to watch the formation of stacken- 
clouds in the morning, and trace them from minute 
specks that seem to form out of the atmosphere, to 
those large masses that move majestically along in 
the wind, and convey water from place to place. 
In fair weather, soon after sunrise a small cloud 



appears ; as this increases, others form near it and 
fall into it as if attracted; a large mass is at length 
upraised, and then all the smaller clouds that form 
in its neighborhood are soon lost, while the mass 
augments ; and the spectator, though he sees not 
the process, feels no doubt that the disappearance 
of the smaller, and increase of the larger cloud, 
must be owing to the larger mass having attracted 
the less into itself But why are the smaller clouds 
lost to the view before they reach and are quite 
drawn into the larger one ? Possibly, when the small 
cloud is very near, with most of its vapors drawn 
away, the rest rush into the larger, as a magnet, 
when it has approached a larger one within a 
certain distance, is forcibly and suddenly attracted. 

When these ephemeral mountains of electrical 
vapor have increased much, as they do toward 
midday, they often unite and form dense, extensive, 
and irregular masses. 

The rapid formation and disappearance of small 
cumuli is a process constantly going on in particular 
kinds of weather, especially when the air is clear 
and dry, with light easterly breezes. These little 
stacken-clouds seem to form out of the atmosphere, 
and to be resolved into it again as rapidly. 



WONDERS OF THE HEAVENS 



341 



The cumulus, then, may either evaporate, change 
into other modifications, or, by uniting with any 
of those that are diflferently electrified, may form 
the sonder-cloud, and ultimately the rain-cloud, 
hereafter to be described. 

Fall-cloud. This kind of cloud rests upon the 
surface of the globe. It is of variable extent and 
thickness, and is called stratus, a bed or covering. 



It is generally formed by the subsidence of vapor 
in the atmosphere, and has, therefore, been de- 
nominated /a//-c/oM(/. This genus includes all fogs, 
and those creeping mists that in summer evenings 
fill the valleys, remain during the night, and 
disappear in the morning. The best time for ob- 
serving its formation is on a fine evening, after a 
hot summer's day. As the cumuli that have pre- 




vailed through the day decrease, a white mist forms 
close to the ground, or extends only for a short 
distance above it. This cloud arrives at its density 
about midnight, or between that time and morning, 
and it generally disappears about sunrise. It is for 
this reason called by some the cloud of night. The 
coming in of autumn is generally marked by a 
greater prevalence and density of this cloud. In 
winter it is still denser. It has often been found 
to be electrified positively. The stratus should not 
be confounded with that variety of the cirrostratus 
which is similar in external appearances ; the test 
to distinguish them is, the stratus does not wet 
objects that it alights upon, the cirrostratus moist- 
ens every thing it touches. 

As the sun sinks the heat is diminished, and the 
low^er atmosphere becomes cooler than that above ; 
the air, no longer capable of containing so much 
vapor in solution as when it was warmer in the 
day, may deposit it in minute particles of water, 
which may descend in the form of stratus. In the 
evening, too, the under atmosphere being as cold, 
or perhaps colder than the upper, the vapor plane 
is not preserved, and stacken-clouds by degrees 
may sink down in dew. Under these circum- 
stances they often appear to evaporate. The 
subsidence at a time when the general dampness 
of the air would afford a passage for its electricity 



to the earth, seems to indicate the agency of that 
fluid in keeping its particles collected inta the 
hemispherical mass in which it usually appears 
during the day. 

The fall-cloud is found to be electrified positive- 
ly, and in general to be highly charged. It has 
been proposed to examine the air above to see 
whether a negative counter-charge can be found. 
Most persons must have noticed the difference 
between the white mists that wet nothing, but 
only leave dew-drops on the herbage, veiling the 
meadows and valleys through a summer night and 
ascending in the morning, and those wet fogs that 
happen at all times of the day, but oftener in the 
morning, which in some places amount to fine rain, 
being known as "the pride of the morning." The 
former are stratus ; the latter, probably, twain- 
clouds. As the temperature decreases in autumn 
the stratus becomes thicker; the rays of the sun 
seem hardly able to overcome it, and it sometimes 
lasts throughout whole days; thus it gave rise in 
the minds of the ancients, whose organization led 
them to express facts metaphorically, to the fable 
of Phoebus and Python. 

In the neighborhood of great cities these fogs, 
impregnated with numerous effluvia and with smoke, 
have a yellow appearance that is explainable ; but 
even in the country the yellow fogs of November 



342 



WONDERS OF THE HEAVENS. 



extend over large tracts of land. Dense fogs also 
happen sometimes, and appear suddenly, in differ- 
ent places ; while at other times fogs continue for 
weeks together. 

SoNDER-cLOUD. This consists of extensive beds 
of a number of little, well-defined, orbicular masses 



of clouds, or small cumuli, in close horizontal oppo- 
sition, but at the same time lying quite asunder, | 
(sonder-doud,) or separate from one another. It is 
to be distinguished from some appearances of the 
cirrostratus which resemble it by the dense and 
compact form of its component nubeculse {little 




clouds.) From the intermediate nature vi' this 
cloud between the cirrus and cumulus, it has been 
called cirrocumulus. The word sonder-cloud is of 
Saxon derivation. 

Sometimes the nubeculae are very dense in their 
structure, very round in their form, and in very 
close opposition.* 

At other times they are of a light, fleecy texture, 
and of no regular form. 

The sonder-cloud of summer is of a middle 
nature between the two last ; its nubeculse vary in 
size and in proximity, and its picturesque appear- 
ance in this season by moonlight, has been well 
described by Bloomfield : — 

" For yet above these wafted clouds are seen, 
In a remoter sky still more serene, 
Others detached in ranges through the air, 
Spotless as snow, and numberless as fair. 
Scattered immensely wide from east to west. 
The beauteous semblance of a flock at rest." 

The formation of this kind of cloud is either 
spontaneous, that is, unpreceded by any other, or 
results from the changes of some other modification. 
Thus the curl-cloud or wane-cloud often chan2:es 
into the sonder-cloud, and the reverse. If it does 

* When this cloud prevails we may, in general, anticipate in 
summer an increase of temperature; in winter it often precedes 
the breaking up of a frost, and is an indication of warm and wet 
weather. 

One variety is very striking before, or about the time of, thunder- 
storms in summer. It is commonly a forerunner of storms, and has 
been remarked as such by the poets. 



not terminate with this kind of change, it subsides 
slowly as if by evaporation. 

In the change from the curl-cloud to the sonder- 
cloud some appearances are presented that cannot 
be referred to either. They generally, however, 
end in a determinable modification, which may be 
called the permanent form, for in this it generally 
remains sometime before it evaporates, or assumes 
another form. The permanent features of the 
sonder-cloud vary at different times, and the varie- 
ties are connected with particular states of the 
atmosphere. In fine, warm weather in summer, 
particularly toward evening, the nubeculse that 
compose this cloud are often large, well-defined, 
and separate from each other: the whole sky is 
sometimes replete with them. This feature is often 
the forerunner of fine, after a continuation of wet 
and variable, weather. It is strikingly contrasted 
to the variety that is composed of very small 
nubeculae, in which the sky seems studded with 
innumerable round, white specks, sometimes of so 
light a texture as to be almost transparent. There 
is a cloud of this sort, which (though its nubeculse 
preserve something of the round shape of sonder- 
clouds) has the light and flimsy appearance, and 
almost the transparency, of one variety of the wane- 
cloud, and it is very difficult to decide what name 



to give It. 



In stormy weather previous to thunder a sonder- 
cloud often appears, whose component nubeculse 



r° 



WONDERS OF THE HEAVENS 



343 



are very dense and compact round bodies in close 
arrangement; the prevalence of this feature, par- 
ticularly when accompanied by the twain-cloud, is 
a sure indication of an approaching storm. The 
sonder-cloud is generally a foreboder of warmth. 
In Germany these clouds are called little sheep. 
In certain weather sonder-clouds rapidly form in 
different places in the sky, and again as rapidly 
subside. 

Wane-cloud. This cloud is distinguishable by 
its flatness, and great horizontal extension in pro- 
portion to its perpendicular height. Under all its 



various forms it preserves this characteristic. It 
often results from the fibres of the cirrus, after 
descending from a higher station in the atmosphere, 
subsiding into strata of a more regularly horizontal 
direction, and hence it is called cirrostratus. As it 
is generally changing its figure, and slowly subsid- 
ing, it has received the name of wane-cloud. It 
originates more frequently from the curl-cloud than 
from any other, and less from the twain-cloud than 
the sonder-cloud. Being once formed, it sometimes 
reassumes the character of the modification from 
which it originated ; but more frequently it evapo- 




rates by degrees, or, by inosculating with some 
other modification, produces the twain-cloud, and 
eventually the rain-cloud. 

Sometimes this cloud is disposed in wavy bars or 
streaks, in close horizontal opposition; and these 
bars vary infinitely in size and color, generally 
blended in the middle, but distinct towards its 
edges, (figure third.) A variety not unlike this is 
the mackerel-back sky of summer evenings. It is 
often very high in the atmosphere. Another com- 
mon variety appears like a long streak, thickest in 
the middle, and wasting away at its edges. This, 
when viewed in the horizon, has the appearance 
of figure fifth. It often seems to lie on the summit 
of the cumulostratus ; in this case, the density of 
the latter increases in proportion as the former 
form and evaporate upon it. The result of this 



intermixture, and the consequent density, is the 
formation of the rain-cloud and the fall of rain. 

Another principal variety of the cirrostratus is 
one which consists of small rows of little clouds, 
curved in a peculiar manner ; it is from this curva- 
ture called cymoid, (figure first.) 

Figure sixth is the representation of a wane-cloud 
changing to a sonder-cloud. Figures second and 
fourth represent wane-clouds seen in profile. 

All clouds are capable of becoming lighter or 
darker according to their position with respect to 
the sun ; the wane-cloud, however, is remarkable 
for exhibiting a great variety of beautiful colors, 
according to its variation in density, to other 
peculiarities, or to its relative position. These 
appearances are best seen in the evening or morn- 
ing, when the sun is near the horizon. They have 



EnxusuoiSBa! 



umrmimysrRMBi^xjsai 



344 



WONDERS OF THE HEAVENS 



been well described by the ancient poets, who 
considered them as precursors of rain and tempes- 
tuous weather; and modern meteorologists have 
confirmed this speculative notion of the ancients, 
and observed the prevalence of the wane-cloud to 
be usually followed by bad weather. 

The most simple form of this cloud is the plane 
sheets. When these are not extensive and are 
seen in the distance, they often look like dense 
streaks drawn along near the horizon, but dis- 
tinguishable from streaks of curl-cloud. It is the 
thin and extensive sheets of the wane-cloud cover- 
ing the heaven before its condensation, in which 
the halo appears. It is this cloud, that, under 
some known circumstances of atmospheric change, 



first in a diffused form, obscures the sky, (dimming 
the light of the sun, moon, or stars, and causing 
such peculiar refractions as mock-suns,) and finally 
becomes mimbiform, and ends in gentle and con- 
tinued rain. The sun often sets apparently shroud- 
ed in a dense feature of this modification, and this 
is a sure indication of a wet morning. 

TwAiN-cLOUD. The base of this modification 
is generally flat, and lies on the surface of an 
atmospheric stratum, the superstructure resembling 
a bulky stacken-cloud overhanging its base in large 
fleecy protuberances, or rising into the forms of 
rocky mountains. Considerable masses of these 
are frequently grouped upon a common stratum or 
base, from which it has been named cumulostratus. 




It derives the other appellation, twain-doud, from 
the frequently visible coalescence of two other 
modifications, as, for example, the curl-cloud and 
the stacken-cloud. Its density is always much 
greater than the stacken-cloud. Cumulostratus 
sometimes forms spontaneously, but is generally 
produced by the retardation of the stacken-cloud 
in its progress with the wind, which then increases 
in density and lateral dimensions, and finally pro- 
trudes over its base in large and irregular projec- 
tions. Sometimes contiguous stacken-clouds unite 
at their bases, and at once become cumulostratus. 
Sometimes the upper currents of air conduct wane- 
clouds near the summits of stacken-clouds, or 
pierce them. 

Cumulostratus often evaporates, sometimes 



changes to stacken-cloud, but in general it ends 
in rain-cloud, and falls in rain. In long ranges of 
these clouds, it has been observed that part has 
changed into rain-cloud, and the rest remained 
unchanged. 

The twain-cloud varies in appearance; some- 
times it overhangs a perpendicular stem, and looks 
like a great mushroom; frequently a long range 
appears together that has the appearance of a 
chain of mountains with silvery tops. Before 
thunder-storms it seems frequently reddish, which 
some have supposed to be caused by its being 
highly charged with the electric fluid. Whether 
this cloud is formed by a visible conjunction of 
different modifications, whether the stacken-cloud 
spontaneously assumes its form, or whether it ap- 



WONDERS OF THE HEAVENS 



345 



pears of itself previously, we must regard it as a 
stage toward the rain-cloud. The very dense and 
black appearance of this cloud, coming up with the 
wind and just ripening into a storm, must be 
familiar to every body. Where the rain has actu- 
ally begun to fall, the blackness is changed for a 
more obscure and gray color. This may be only 
the effect of the interposed water of the falling 
rain; but if not, and if the rain-cloud be affected 
by an intenser union of the watery particles, the 
blackness of the previous twain-cloud must depend 
on some other principle. 

Rain-cloud. This is not a modification depend- 
ing upon a distinct change of form, but rather from 
increase of density and deepening of shade, in the 



twain-cloud, indicating a change of structure which 
is always followed by the fall of rain. This has 
been, therefore, called nimbus, (a rainy black cloud.) 
Any one of the preceding six modifications may 
increase so much as to obscure the sky, and, 
without falling in rain, "dissolve," and "leave not 
a rack behind." But when the twain-cloud has 
been formed, it sometimes goes on to increase in 
density and assume a black and portentous dark- 
ness. Shortly afterwards the intensity of this 
blackness yields to a more gray obscurity, which is 
an evidence that a new arrangement has taken 
place in the aqueous particles of the cloud; the 
nimbus is formed, and rain begins to fall. The 
accompanying plate represents a nimbus pouring 




rain. The shower continues until another interior 
change succeeds, when the nimbus is extinct, and 
more or less of other modifications reappear ; the 
curl-cloud, wane-cloud, or perhaps the sonder- 
cloud is seen in the higher regions of the atmo- 
sphere, and the remaining stacken-cloud, no longer 
retarded, sails along in a current of wind nearer 
the earth. These effects may be satisfactorily 
observed when showers fall at a distance; the 
nimbus can then be seen in profile, and the process 
of its formation and destruction followed through 
all its stages. 

Stacken-clouds may be seen rising into moun- 
tains and becoming twain-clouds, while long strata 

44 



of wane-clouds permeate their summits, and the 
whole phenomenon has the appearance of a range 
of mountains transfixed by the mighty shafts of a 
giant. After having existed for some time in this 
form, they become large and irregular, and get 
darker by intensity, till all seem concentrated in a 
dense black mass, with a cirrose crown extending 
from the top, and ragged stacken-clouds entering 
from below, and the whole eventually resolves 
itself into rain. 

A division may be made of rain-clouds into 
three kinds: — Those that result from the visible 
union of distinct clouds; those that follow the in- 
terposition of moisture between distinct clouds ; and 



346 



WONDERS OF THE HEAVENS. 



those that appear to form spontaneously in the 
air without being preceded by either of the above 
phenomena. 1st. If a curl-cloud, after it has 
ceased to conduct electricity, should receive from 
either mass of air (between which it may have 
been conducting) an electric charge, it would lose 
its cirriform figure and take some other, perhaps 
that of a sonder-cloud, and by degrees sink down 
toward the earth. Under such circumstances, it 
may come in contact with a stacken-cloud rising 
from below. The result would be a sudden mix- 
ture of both clouds into a dense mass of rain-cloud, 
which would resolve itself into a gentle shower, 
and thus the union of two clouds would effect 
apparently the destruction of both. Such showers 
are of short duration, because the rain-cloud thus 
formed is circumscribed by dry air, and has no 
source of supply. 

2. Previous to rain the stacken-cloud in the 
lower atmosphere changes its appearance, becomes 
denser, irregular in shape, and rock-like in super- 
structure, with fleecy protuberances about its base, 
and by degrees a complete twain-cloud. While 
this process is going on, curl-clouds, wane-clouds, 
or sonder-clouds, that have previously been seen 
above, are to all appearance lost, as if they had 
suddenly evaporated. The air Avill now be found 
damper, and there is frequently a visible misti- 
ness above. Thus, the surrounding air being damp, 
the process continues, and affects clouds more and 
more distant, and the result is nimbus or rain. 

3. It appears, then, that the cause of union be- 
tween two differently electrified strata of clouds, is 
the moisture of the interposed atmosphere; and 
this humidity may take place, either in consequence 
of the dispersion of some cloud from a cessation of 
the electric actions, or by a more general deposi- 
tion of haze from the over-saturated air. Either 
of these might cause a union, and the production 
of a rain-cloud. This may explain the cause of 
that rain-cloud which is unpreceded by other 
clouds. For if the air, from unknown causes, can 
so deposit watery particles which may be diffused 
through a large mass of air, if the large tracts of 
air, before dry and consequently electric, should 



have a plus and minus state, the watery particles 
would also receive such a division of electricity. 
But these electricities, having now (by the general 
moisture) a communication almost as soon as form- 
ed, might unite and cause the moisture to descend 
as rain. 

This process would be comparatively slow and 
progressive, and thus we may account for what has 
been called by some "the spontaneous formation 
of rain-clouds," and by others "the gradual con- 
densation of the air into rain," that lasts whole 
days, affording an example of the slow and gentle 
operation of the same causes, which, when effected 
rapidly, produce the phenomena of violent thunder- 
storms. 

Masses of clouds frequently appear, not referable, 
for a time, to any of the preceding modifications ; 
but if they last long enough, even these generally 
break out into some modification ultimately. 

It is not always an easy matter for an inexperi- 
enced eye to judge how every cloud it sees should 
be classed. There are intermediate varieties of 
curl-clouds, wane-clouds, and sonder-clouds, which 
approach so much to the nature of each other, that 
the assignation of a name becomes very difficult. 
A tendency to the orbicular arrangement while the 
nubeculge are kept asunder, is the distinguishing 
trait of the sonder-cloud; but clouds sometimes 
appear having somewhat of this kind of arrange- 
ment, yet so light in their texture as to partake 
almost of the nature of the wane-cloud. There 
are many varieties with these indeterminable fea- 
tures. A flimsy cloud of this kind is often seen in 
the clearer intervals of rainy weather, which gives 
the idea of the flowers of the cauliflower. The 
innumerable little round spots of clbud which 
sometimes cover a great extent of sky are some- 
times of this flimsy and almost transparent struc- 
ture, while at other times they are denser, and 
therefore more decidedly sonder-clouds. In some 
kinds of weather, a cloud is seen (covering a great 
part of the sky) which has the thin and transparent 
texture of wane-cloud, but the nubeculae have the 
large and rounded form of sonder-cloud. It seems 
to differ from the latter in being shallow and 



WONDERS OF THE HEAVENS 



347 



flimsy, and from the former in having a rounded 
outline. Among the sportive and amusing features 
exhibited, vv^e have sometimes long, tapering col- 
umns, horizontal or inclined, of a cloud composed 
of sonder-cloud nubeculae, and sometimes of those 
of a sort of wane-cloud like little freckles, or like 
numerous small streaks arranged in row^s. These 
little bunches are generally in a plane, but have 
sometimes appeared (perhaps an optical illusion) 
in a roundish column, giving a faint resemblance to 
the tail of an armadillo. Forster once saw a 
column of this sort inclined, curved, apparently 
pendant from a variety of curl-cloud, and colored 
purple and lake by the setting sun. In the large 
and long beds of nubeculae which frequently float 
gently over us in summer, there are sometimes 
wane-clouds and sonder-clouds in the same bed. 
These change by degrees from one to another, 
and there are intermediate features more or less 
evident in the same mass of floating waters. 

Scud. We may observe after showers, when the 
rain-cloud seems to be spent, and the separate 
modifications reappear in their different stations, 
loose flocky detachments of clouds flying along in 
the wind, and generally low down. These seem 
like broken fragments of the rain-cloud, and are 
called scud by the seaman. They often fly along 
in a lower current of wind at a time when large 
mountainous twain-clouds and stacken-clouds ap- 
pear somewhat higher and more stationary, and 
when flimsy features of wane-cloud, sonder-cloud, 
and curl-cloud are visible in regions still more ele- 
vated. When this scud is abundant, we may rea- 
sonably expect a return of the showers. 

The Color of Clouds. Clouds refract and re- 
flect a great variety of beautiful tints, the shades of 
which vary according to their relative position with 
respect to the sun, but the color seems also to de- 
pend on the kind of cloud and the degree of its 
density. The wane-cloud exhibits the most beau- 
tiful and varied colors. Different shades of purple, 
crimson, lake and scarlet, are the most common. 
The haze, with a horizontal sun, refracts different 
colors at different times, viz. yellow, orange, more 
or less of a golden hue, red, lake, and sometimes 



a brownish color. Sometimes several colors are 
seen at once. Clouds of the same variety at 
different times show different colors, though they 
may be in nearly the same situation with respect 
to the sun. Sometimes they appear richly colored, 
at other times scarcely colored at all, a circum- 
stance that makes it questionable whether the 
color is from the cloud itself, or the cloud only 
reflects light already colored by refraction in its 
passage through the haze of the atmosphere. The 
former is probably the case ; for different clouds, in 
nearly the same situation with respect to the sun, 
show different colors at the same time. Yet the 
colors refracted by the haze are very various. 
Sometimes its tints in the twilight come on so sud- 
denly, and are so circumscribed, as to induce a 
belief that very sudden and partial changes take 
place in the atmosphere at evening. There is 
frequently a deep golden orange close to the hori- 
zon ; a crimson blush above it fading into purple 
and dark blue; about it, on each side, a whitish 
transparent appearance, or a lively greenish blue, 
or the light prismatic blue ; and all these vary as 
the sun descends farther below the horizon. 

These and other beautiful appearances of diverg- 
ing streaks, bars, and spots, may often be seen 
with the sun near the horizon; we notice them 
chiefly in the evening, because we do not rise early 
enough in the morning; but they display nearly 
the same degree of beauty, with some variety of 
appearance, when they usher forth the dawn rising 
from the couch of sable night, as when they throw 
their painted canopy over the declining sun, or 
mark the spot where he sank beneath the western 
hills, till they gradually fade away and are lost in 
the universal gloom. 

The Height of Clouds. The average elevation 
of the different modifications is different. Accord- 
ing to Howard, the curl-cloud is the highest, the 
sonder-cloud next, then, in succession downward, 
the wane-cloud, the stacken-cloud, and fall-cloud. 
The twain-cloud is of vast vertical dimensions ; 
when it forms on a stacken-cloud, the top of it ap- 
pears to rise higher, and the base is generally 
lower, than those of the stacken-cloud. The nim- 



tha w Lam a a-.w ^iKfipVJn fr'^fYg 



348 



WONDERS OF THE HEAVENS 



bus, which is the resolution of clouds into rain, 
may be considered as having its base on the earth, 
and its summit at the end of the fibres of its cirrose 
crown. The modifications have different elevations 
at different times, and they are sometimes inverted. 
Sonder-cloud may at times be seen under a spread- 
ing sheet of curl-cloud of a milky appearance, 
that looks like a bass-relief The long lines of 
curl-cloud have been found by geographical ob- 
servation to be very high. Saussure speaks of the 
great height of certain clouds, that, from his descrip- 
tion, must have been mottled beds of wane-cloud; 
and Dalton mentions that mackerel-back clouds 
have appeared from the tops of high mountains 
almost as high as from the ground. Aeronauts 
have generally ascended much beyond the stack- 
en-clouds, but it is probable that there are 
clouds much higher up than any balloon ever as- 
cended. 

Those who have been on the tops of mountains, 
have spoken of having seen clouds pass below 
them ; but, being unacquainted with the peculiarities 
of clouds, and inattentive in their observations, 
their accounts have been of little value in ascer- 
taining the general height of the modifications. 
Indeed, nothing very satisfactory has been decided 
on this head. 

Structure and Buoyancy of Clouds. Do the 
particles remain afloat in the air, or only gravitate 
very slowly toward the ground? On what pecu- 
liarity of structure does their comparative levity 
depend? These questions can be answered only 
with conjecture. De Luc and Saussure have sup- 
posed the particles to be hollow vesicles, and if 
these vesicles contain an aeriform fluid lighter 
than common air, they would be buoyant, and float 
in the atmosphere. This, however, is but conjec- 
ture, and nothing is certainly known of the struc- 
ture of clouds. But that the structure of different 
clouds is very different, is manifest from their 
different refracting and reflecting powers, produc- 
ing the various appearances of halos, coronas, 
mock-suns, &c., on different occasions, as well as 
from the different appearances of the clouds them- 
selves. 



SECTION III. 

Division of falling meteors — Phenomenon witnessed at Leeds, Eng- 
land, in 1710— In March, 1719, all over England— In March, 1813, 
at New Haven, Connecticut — In Vermont, January, 1817, and 
March, 1822 — In various places, November 13th, 1833— Olmsted's 
theory respecting its cause — Repetition of the meteoric phenome- 
non in 1834, 1835, 1836— Arago's theory— Ignis fatui, or Will 
o'-the-wisps. 

We have thought best to class under two heads 
those luminous bodies which occasionally make 
their appearance in our atmosphere, sometimes 
startling us with the rapidity of their motion anH^ 
the brightness of their beams, at others simply 
exciting our curiosity or our admiration. In the 
first place we shall treat of those which leave no 
permanent trace behind them, under the denomi- 
nation of shooting stars and Will-o'-the-wisps — 
leaving for another section those meteors which 
project stones or metallic substances to the earth 
under the name of aerolites, using meteor as a 
term common to both. 

A strange meteor was seen at Leeds (England) 
in 1710, on Holy Thursday; the common people 
called it a flaming sword. It was seen not only in 
the neighboring towns, but far north, and more 
than fifty miles south of Leeds. It appeared at 
Leeds at a quarter after ten at night, and took a 
northerly course. It was broad at one end, and 
small at the other, and was by some thought to 
resemble a trumpet moving with the broad end 
foremost. Its light was so great as to impart a 
shadow to objects around. All the persons who 
saw it (though many miles distant from each other) 
thought it fell very near them, and that it went off" 
with bright sparklings at the small end. A cler- 
gyman asserted that it was the strangest illusion 
that ever happened to him if that meteor was not 
extinguished within a few paces of him, and yet 
others saw it, a few moments after, many miles 
farther north. 

On the 19th of March, 1719, a wonderful meteor 
was seen all over England. Suddenly a great 
light, much beyond that of the moon, which shone 
very bright at the time, was visible in the west to 
persons in London, at about a quarter after eight 
in the evening. It seemed at first near the seven 



^^ 



WONDERS OF THE HEAVENS. 



349 



stars, whence it moved after the manner of (but 
more slowly than) a shooting star, in an apparent 
right line, passing beyond and below the stars in 
Orion's Belt, thence toward the south-west. The 
long stream appeared to be branched about the 
middle, and the meteor as it went on became pear- 
shaped. It afterward became more spherical and 
larger, though not so large as the full moon ; the 
color of it was whitish, of a most vivid, dazzling 
lustre, which seemed in brightness to resemble, if 
not to surpass that of the sun, beheld by the naked 
eye, in a clear day. This brightness obliged 
observers to turn away their eyes several times, as 
well when it was a stream, as when it was a pear 
and a globe in form, however great might be their 
desire to observe it strictly. In the space of half 
a minute it seemed to move twenty degrees, and to 
go out as many degrees above the horizon. It left 
behind it a track of a faint reddish yellow color, 
that remained visible more than a minute, seemed 
to sparkle, and kept its place without falling. The 
sparks issuing from this train appeared like those 
which come from red-hot iron, when beaten on an 
anvil. All the observers agreed in this, " that the 
splendor of the meteor was, at the least, nearly 
equal to that of the sun," so that the candles 
within-doors seemed to give no light, and not only 
all the stars became invisible, but the moon, then 
nine days old, and near the meridian, was so far 
dimmed as to be scarcely perceptible, (the sky all 
the while being perfectly clear,) and wholly incapa- 
ble of causing any object to cast a shadow. For a 
few seconds the night in all respects resembled 
perfect day; — this was about a quarter after eight 
o'clock. The velocity of the fire-ball was com- 
puted by Halley to be at least three hundred miles 
a minute, a swiftness almost incredible, so great 
that if a heavy body were projected horizontally 
with the same, it would not descend by its gravity 
to the earth, but move round in a perpetual orbit 
resembling that of the moon. 

Of several accidents that were said to have at- 
tended its passage, many were the effects of fancy ; 
such as hearing it hiss, as if it had been very near 
the observer. Some imagined that they felt the 



warmth of its beams, and others asserted that they 
were scalded by it. One thing is certain, viz. an 
extraordinary noise followed the explosion. There 
was heard a sound like the report of a heavy can- 
non, or rather of a broadside, at some distance, 
that was followed by a noise similar to the 
rattling of small-arms discharged promiscuously. 
These sounds were attended with an uncommon 
tremor of the air ; the windows and doors of the 
dwelling-houses were sensibly shaken, and accord- 
ing to some, even the houses themselves, beyond 
the usual effect of cannon, though near. The phe- 
nomenon was attributed by Halley to the unusual 
and long-continued heat of the preceding summer. 
At New Haven, on March 21st, 1813, a little 
before ten o'clock, a meteor was observed. The 
sky was overcast, yet the covering was everywhere 
thin, and in the north, where the meteor appeared, 
the stars were in full view. The observer was 
looking eastward when the light first appeared, 
and he supposed it to be caused by lightning. 
When the meteor was first seen, it was about 
thirty-five degrees above the horizon, and the 
direction of its track was estimated to be about 
north twenty degrees east. Its figure was nearly 
that of an ellipse, with the ends slightly pointed. 
Its longest apparent diameter was about equal to 
the apparent diameter of the moon on the merid- 
ian ; its shortest diameter about three-fourths of 
that quantity. The color of the body was similar 
to that of the moon, yet of a more decided yellow. 
A train of light was formed behind it of ten or 
twelve degrees in length. This was broadest near 
the body, and decreased in breadth very slowly for 
two-fifths of its length, after which it was a uni- 
form stripe of light, about as wide as the apparent 
diameter of Venus. The light was so powerful 
that all objects around cast distinct shadows. 
Numerous star-like sparks continually issued from 
the body, and a short time before its disappearance 
three larger fragments were thrown from it, two 
apparently as large as Venus, the third much 
larger. Each fragment as it moved became less 
and less distinct, until it disappeared entirely. 
The last of these continued visible until within 



350 



WONDERS OF THE HEAVENS 



twenty degrees of the horizon. The meteor itself 
disappeared as suddenly as if in one indivisible 
moment it had passed into a medium absolutely 
opaque, or as if it (all at once) left the atmo- 
sphere ; but a few moments afterward there was a 
distinct and somewhat extensive illumination over 
that part of the sky for about a second, as if the 
light of the departing body had been reflected from 
some unknown surface to the earth. When the 
meteor disappeared, it was about thirty degrees 
above the horizon. Within eight or ten minutes 
after its disappearance there was a very loud and 
heavy report, accompanied with a sensible jar. 
The report did not resemble either thunder or the 
roar of cannon, but was louder, shorter and sharper 
than either. 

On the evening of January 8th, 1817, during a 
rapid fall of moist snow attended with repeated 
claps of thunder, lights or luminous appearances 
were seen in the atmosphere in many places on the 
Green Mountains. In all these places the lights 
were described as having the same appearance. 
They were observed on the tops of bushes, fences, 
houses, &c. Some persons represented them as 
appearing like the blaze of candles, but all agreed 
that they were luminous spaces which appeared to 
rest on pointed or elevated substances. In some 
instances, persons who were travelling suddenly 
observed a light surrounding their heads ; in others, 
they were completely enveloped in a light but little 
less than the ordinary light of the sun. Several 
persons found, when they raised their hands, that 
the light appeared to stream from their fingers. 
Phenomena like these had seldom been seen in 
that vicinity. We have no accounts of such since 
the first settlement of the country. As usual, for 
want of more satisfactory explanations, these ap- 
pearances were attributed to electricity. 

March 9th, 1822. An observer at Burlington, 
Vermont, had his attention arrested by what is 
commonly called a shooting star, no way differing 
from such as frequently appear in considerable 
numbers. When he first saw it, he thought it about 
in the centre of a triangle formed by lines joining 
Mars, Castor, and Procyon. It moved south-west- 



erly, passing a little south-east of Procyon, and 
when about one-third of the way from Procyon to 
Sirius, it suddenly burst out in great splendor, and 
continued its course flashing and sparkling east of 
Sirius, and was apparently extinguished near the 
tops of some trees about twenty rods distant, con- 
siderably above the mountains. Its motion seemed 
perpendicular to the horizon. Its disc was nearly 
circular, its absolute diameter was estimated at 
about one-third of a mile, and its velocity as 
greater than that of the earth in its orbit. 

Meteoes of November 13, 1833. — New Haven. 
About daybreak, the sky presented a remarkable 
exhibition of fire-balls commonly called shooting 
stars. To form some idea of the phenomenon, the 
reader may imagine a constant succession of fire- 
balls resembling rockets, radiating in all directions 
from a point in the heavens a few degrees south- 
east of the zenith, and following the arch of the 
sky toward the horizon. Around this point was a 
circular space of several degrees, within which no 
meteors were observable. The balls usually left 
after them a vivid streak of light, and before they 
disappeared exploded, or suddenly resolved them- 
selves into smoke. No report, however, was 
heard. 

Beside these, the atmosphere exhibited phos- 
phoric lines, following in the train of minute points 
that shot off" in the greatest abundance in a 
north-westerly direction. The light of these trains 
was not unlike that produced by writing with a 
stick of phosphorus on the walls of a dark room. 
Between these two varieties, the spectator was 
presented with meteors of various sizes and degrees 
of splendor; some were mere points, others were 
larger and brighter than Venus, and one was 
judged to be nearly as large as the moon. One 
ball, that shot off" in a north-westerly direction, and 
exploded a little to the north of the star Capella, 
left, just behind the place of its explosion, a phos- 
phorescent train of peculiar beauty. This line 
was at first nearly straight, but shortly began to 
contract in length, dilate in breadth, and to assume 
the figure of a serpent drawing itself up, until it 
appeared like a small luminous cloud of vapor. 



WONDERS OF THE HEAVENS 



351 



The light of the meteors was usually white, but 
was occasionally prismatic, with a preponderance 
of blue. 

Boston. The sky was clear, excepting near the 
horizon, where, in the east, there were a few 
streaks of cloud, and in the south-east and south 
the round heads of a range of dark, heavy clouds 
were just visible above the horizon. There was, 
however, a vapor visible round the horizon, which 
in the south-east assumed a very beautiful ap- 
pearance during ten minutes, about half an hour 
before sunrise. The direction in which the mete- 
ors moved was almost exactly downward, (and not 
oblique, as usually seen,) except in two instances, 
when the course was horizontal, nearly in a 
straight line, from north-east to south-west, and 
these two meteors were high and small. All the 
meteors left luminous white traces, which generally 
appeared to be about a yard in length. 

Similar phenomena, adds the Boston writer, have 
occasionally occurred elsewhere, and have been 
called showers of fire, to which indeed this had a 
perfect resemblance. One instance occurred about 
eighty years since in South America, at Quito, 
when so many falling stars were seen above the 
volcano of Gayambo, as led the people to imagine 
that the mountains were in flames. A more ex- 
tensive and remarkable phenomenon of this kind 
occurred on the night of November 12th, 1799, and 
was seen at Cumana. It happened near morning, 
when thousands of meteors succeeded each other 
during the space of four hours. There was not a 
place in the firmament equal in extent to three 
diameters of the moon, that was not filled with 
burning stars. They were of different sizes, and 
left luminous traces of from five to fifteen degrees 
in length. They were seen by almost all the 
inhabitants of Cumana, the oldest of whom assert- 
ed that the great earthquake of 1766 was preced- 
ed by similar phenomena. The fishermen said 
that the fire-works began at one o'clock, and some 
of the meteors were thought to have been seen a 
quarter of an hour after sunrise. 

West Point. The air was very clear, and there 
was a perceptible and constant light like twilight 



given out from the numerous luminous bodies. 
The greater part of these bodies were like stars 
suddenly lighted up while in a state of rapid mo- 
tion, shooting a certain distance, and gone in a 
second. Another class of luminous bodies, larger 
in diameter, but equally transient in continuance, 
and less frequent, shot along like falling lamps, 
followed by a small, short, and pointed flame, so 
brilliant as to pain the sight. These might be 
compared to the morning star in sensible magnitude, 
and to lightning in brilliancy. One larger body fell 
vertically west of north. It was a deep-red, fiery 
ball, of perhaps one-fifth the moon's apparent diame- 
ter : It descended to the visible horizon, and left 
a train of a few degrees in extent, luminous, and 
striped with prismatic colors, one edge being red, 
and the other greenish blue. Occasionally, in the 
smaller bodies also, the prismatic colors were de- 
veloped; and about the time when the morning 
light was beginning to make the fainter phenomena 
invisible, many meteors were observed of a faint 
but decided green. 

There was a point a few degrees south and east 
of the zenith, which was evidently the emanating 
point of all the apparent motions. In the vicinity 
of this point a few star-like bodies were observable, 
possessing very little motion, and leaving very 
little trace, but in their aspect they were such as 
if a small nebula had softly swelled out from the 
heavens, gently elongated its figure, and then as 
gently subsided. 

Farther off", the motions were more rapid, and 
the traces longer; and the most rapid of all, and 
the longest in their traces, were those that origi- 
nated but a few degrees above the horizon, and 
descended to it. In these, the aspect might be 
compared to that of flaming sparks driven swiftly 
athwart the sky by a strong wind. The number 
of shooting bodies that passed in the heavens on 
the morning of the 13th, though necessarily the 
subject of conjecture to a considerable extent, was 
estimated without extravagance at ten thousand in 
the course of a single hour. 

Annapolis. Many persons thought a shower of 
fire was falling, and became exceedingly alarmed. 



352 



WONDERS OF THE HEAVENS 



The light was so intense that sleeping apartments 
were strongly illuminated, and some were aroused 
under the apprehension that their dwellings were in 
flames. The meteors were most numerous an hour 
before dawn, but a number of shooting stars were 
visible as early as two o'clock in the morning. 
The phenomenon must have therefore continued, 
more or less vividly, for four or five hours. The 
statements of observers agree entirely as to the 
almost infinite number of the meteors, and, in the 
words of many, "they fell like flakes of snow." 
Those who saw it to the best advantage agree as 
nearly as could be expected, making allowance, as 
we should, for the probable existence of extraor- 
dinary excitement. Several of the meteors appear- 
ed to burst into numerous small stars as they fell, 
and it was asserted that some fell to the earth and 
rebounded into the air. This was probably an 
optical deception. The accounts differ as to the 
size of the meteors. One in particular was stated 
by some observers to be as large as the moon, 
while to others it appeared considerably smaller. 
So also the most brilliant of them was said to have 
been visible for more than a minute, though it 
probably could not have been visible beyond a few 
seconds. It was evident that this meteor was of 
an uncommon size, and that it was seen much 
longer than is usual for these transitory scintilla- 
tions. It was certain that one of the trains con- 
tinued faintly visible about thirty seconds. No 
audible explosion attended any of the meteors. 
The whole scene was like a perfectly silent and 
simultaneous dance of the stars. 

Emmittshurg. It would be difficult for one who 
did not witness the grand exhibition, to conceive 
the effect of the uninterrupted succession of innu- 
merable meteors, proceeding from a point so nearly 
vertical toward the whole circumference of the hori- 
zon, and this too during the stillness of night, with 
an atmosphere perfectly transparent. It could be 
compared only to a continued discharge of fire- 
works, occupying the whole visible heavens. Their 
light was similar to what has heretofore been 
noticed on analogous occasions, white, with a tinge 
of blue, comparable to the flame of burning zinc. 



Worthington, Ohio. As witnessed from that 
place, the meteors seemed to diverge from a com- 
mon centre some fifteen degrees south-east of the 
zenith, but it is probable that this apparent diverg- 
ence was an illusion, and that their true courses 
were nearly parallel. A luminous spot or ring 
would frequently appear for a moment near the 
point whence they seemed to emanate, which was 
unquestionably caused by a coincidence of the 
course of the meteor with the line of observation. 

Augusta, Georgia. It seemed at first as if 
worlds upon worlds were rushing like a whirlwind 
toward our globe from the infinity of space ; then 
as if the firmament was slowly melting with fervent 
heat, and the stars descending like snow-flakes to 
the earth; until again some fiery sphere would 
start from its orbit, blazing and hissing through the 
vast expanse, and sweeping worlds from their 
places, or rather hurling whole systems from exist- 
ence in its mad career. The light exhibited was 
different in the different meteors, and even in the 
same meteor at different times. In some the fire- 
ball gave out a pale blue or green light, while the 
train would be orange or intensely white, and soon, 
by constant changes, exhibiting all the prismatic 
colors. Occasionally one would dart forward, 
leaving a brilliant train three or four inches in 
breadth, that would gradually extend in width 
to three or four feet, and remain visible nearly 
fifteen minutes. By far the most brilliant one 
seen occurred a few minutes after five in the 
morning, and seemed by its splendor to announce 
the close of this grand exhibition of heavenly 
fire-works. It seemed to pass from south-east to 
north-west, the ball being apparently five or six 
inches in diameter, with a train from thirty to forty 
feet long ; the latter, immediately on the passage 
of the meteor, assuming a serpentine form, and 
diflfusing a light upon the earth equal at least to 
that of the full moon, and remaining intense for 
forty or fifty seconds. 

Bowling Green, Missouri. Around the firma- 
ment, thicker than the stars themselves, which 
were uncommonly bright and beautiful, were be- 
held innumerable fire-balls of a pale white color, 



WONDERS OF THE HEAVENS 



353 



rushing down, and, to appearance, across the sky, 
drawing after them long, luminous traces, which 
clothed the whole heaven in awful majesty. 

On comparing the accounts that were given of 
the "falling stars" in various places, it is found 
that the appearances were everywhere nearly the 
same, being, with slight variations, as follows: — 
The meteors began to attract notice by their fre- 
quency as early as nine o'clock on the preceding 
evening, the exhibition became strikingly brilliant 
about eleven, but most splendid of all about four 
o'clock, and continued, with but little diminution, 
until merged in the light of day. A few large 
fire-balls were seen even after the sun had arisen. 
The entire extent of the exhibition covered no in- 
considerable portion of the earth's surface. It has 
been traced from the longitude of sixty-one degrees 
in the Atlantic ocean, to longitude one hundred 
degrees in central Mexico, and from the North 
American lakes to the southern side of the island 
of Jamaica. It was not seen, however, anywhere 
in Europe, nor in South America. Everywhere 
within the above-named limits, the first appearance 
was that of fire-works of the most imposing gran- 
deur, covering the entire vault of heaven with 
myriads of fire-balls resembling sky-rockets. On 
more attentive inspection, it was seen that the 
meteors exhibited three distinct varieties, the 
first consisting of phosphoric lines, apparently 
described by a point ; the second, of large fire- 
balls, that at intervals darted along the sky, leaving 
luminous trains that occasionally remained in 
view for a number of minutes, and, in some cases, 
for half an hour or more; the third, of undefined 
luminous bodies, that remained nearly stationary 
in the heavens for a long time. Those of the first 
variety were the most numerous, and resembled a 
shower of fiery snow driven with inconceivable 
velocity to the north of west. The second kind 
appeared more like falling stars, giving to many 
persons the impression that the stars were actually 
falling from the sky, a spectacle which was contem- 
plated by the more unenlightened beholders with 
great amazement and terror. These fire-balls 

were occasionally of enormous size. Dr. Smith, 

4.5 



of North Carolina, describes one that appeared 
larger than the full moon rising. "I was," says 
he, "startled by the splendid light in which the 
surrounding scene was exhibited, rendering even 
small objects quite visible." 

One of the most remarkable circumstances at- 
tending this display was, that the meteors all 
seemed to emanate from one and the same point ; 
that is, if their lines of direction had been continued 
backward, they would have met in the same point, 
a little south-east from the zenith. They set out 
at different distances from this point, and, following 
the arch of the sky, ran along the vault with im- 
mense velocity, describing, in some instances, an 
arc of thirty or forty degrees in less than four 
seconds. The trains which they left were com- 
monly white, but were sometimes tinged with 
various prismatic colors. One ball, that shot off in 
the north-west direction, and exploded a little 
northward of the star Capella, left, just behind the 
place of explosion, a phosphorescent train of pecu- 
liar beauty. The line of direction was at first 
nearly straight ; but it soon began to contract in 
length, to dilate in breadth, and to assume the 
figure of a serpent drawing himself up, until it 
appeared like a small luminous cloud of vapor. 
This cloud was borne eastward, (by the wind, as 
was supposed, which was blowing gently in that 
direction,) opposite to the course in which the meteor 
had proceeded, remaining in sight several minutes. 

Of the third variety of meteors, the following 
are remarkable examples. At Poland, Ohio, a 
luminous body Avas distinctly visible in the north- 
east for more than an hour. It was very brilliant, 
in the form of a pruning-hook, and apparently 
twenty feet long, and eighteen inches broad. It 
gradually settled towards the horizon until it dis- 
appeared. At Niagara Falls, a large, luminous 
body, shaped like a square table, was seen nearly 
in the zenith, remaining for some time almost sta- 
tionary, emitting large streams of light. At 
Charleston, S. C, a meteor of extraordinary size 
was seen to course the heavens for a great length 
of time, and then was heard to explode with the 
noise of a cannon. 



354 



WONDERS OF THE HEAVENS 



The apparent radiant, or the point from which 
the meteors seemed to emanate, was observed, by 
those who fixed its position among the stars, to be 
in the constellation Leo. At New Haven it ap- 
peared in the bend of the sickle, (a collection of 
stars in the breast of Leo,) a little to the westward 
of the star Gamma Leonis. By observers at other 
places remote from each other, it was seen in the 
same constellation, although in different parts of it, 
a change of position supposed to be owing to the 
effect of parallax. An important observation, con- 
firmed by the concurrent testimony of all the ob- 
servers who remarked the position of the foregoing 
radiant point among the fixed stars, is, that this 
point was stationary among the stars during the 
whole period of observation; that is, that it did 
not move along with the earth in its diurnal revo- 
lution eastward, but accompanied the stars in their 
apparent progress westward. 

According to the testimony of by far the greater 
number of observers, the meteors were unaccom- 
panied by any peculiar sound; but, on the other 
hand, such a sound, supposed to proceed from the 
meteors, was said to be distinctly heard by a few 
observers in various places. It is well known, 
however, that persons unaccustomed to making 
observations in the stillness of night are apt, when 
listening at such times, to hear sounds which they 
associate with any remarkable phenomenon that 
happens to be present, although wholly unconnect- 
ed with it. The question, therefore, whether any 
sound proceeded from the meteors, must rest for 
its decision on the circumstances of the case, such 
as the peculiarity of the sounds, and their uniform- 
ity as described by different observers. In the 
present case, the sounds supposed to have been 
heard by a few observers are represented either as 
a hissing noise like the rushing of a sky-rocket, or 
as slight explosions like the bursting of the same 
bodies. These comparisons are thought to occur 
too uniformly, and in too many instances, to permit 
the supposition that they were either imaginary, or 
were derived from extraneous sources. 

It is not held as a fact well established, that any 
substance reached the ground which can be consid- 



ered as a residuum or deposit from the meteors, 
although indications of such a substance were sup- 
posed to be discovered by different observers. 

A change of weather from warm to cold accom- 
panied the meteoric shower, or immediately follow- 
ed it. In all parts of the United States, this change 
was remarkable for its suddenness and intensity. 
In many places, the day preceding had been un- 
usually warm for the season; but before morning 
a severe frost ensued, unparalleled for the time of 
year. Indeed, the seasons and atmospheric changes 
exhibited remarkable anomalies long after that 
period, a fact which it may be well to place on 
record, to compare with future observations, al- 
though it may be impossible to decide, at present, 
whether or not these irregularities had any connec- 
tion with the phenomena in question. Thus, at 
Michilimackinac, so uncommonly mild was the 
season throughout the latter part of November 
and the whole of December, that the Indians made 
maple sugar during this month, and the contiguous 
lakes remained unfrozen as late as the 3d of Janu- 
ary. At the same period, the season in the south- 
western states, as far as New Orleans, was unusu- 
ally cold. In most parts of New England, an 
uncommonly mild winter was succeeded by a 
remarkably cold and backward spring, requiring 
domestic fires to be kindled throughout the month 
of May, and frequently in the month of June. A 
succession of gales commenced about the time of 
the meteoric shower, first in the Atlantic Ocean, 
and afterwards in various parts of the United States, 
almost unequalled in this country for their frequency 
and violence. 

In entering on the explanation of these mysteri- 
ous phenomena, it is argued, in the first place, that 
the meteors had their origin beyond the limits of 
our atmosphere; that they, of course, did not 
belong to this earth, but to the regions of space 
exterior to it. All bodies near the earth, including 
the atmosphere itself, have a common motion with 
the earth round its axis from west to east ; but the 
radiant point that indicated the source from which 
the meteors emanated followed the course of the 
stars from east to west ; therefore it was independ- 



WONDERS OF THE HEAVENS 



355 



ent of the earth's rotation, and consequently at a 
great distance from it, and beyond the limits of the 
atmosphere. 

Having established this point, the next inquiry 
is. What is the height of the place whence the 
meteors proceeded; that is, the height of the me- 
teoric cloud (so to speak) above the surface of the 
earth? If this cloud were not too distant from the 
earth to have a parallax, spectators remote from 
each other would refer it to different points in the 
heavens. If, for example, an observer at Boston 
marked the position of the cloud by a certain star, 
one in South Carolina would refer it to a point 
farther north, and one in Ohio would see it farther 
east. The former change of place is called parallax 
in declination, and the latter parallax in right ascen- 
sion; and a parallax either way affords the means 
of estimating the height of the object above the 
surface of the earth, in the same manner as we 
estimate the height of a common cloud. 

Now it has been ascertained that observations 
made in different latitudes indicated a correspond- 
ing parallax in declination ; and these observations, 
being collected and carefully compared with each 
other, give an average distance from the surface of 
the earth of two thousand two hundred and thirty- 
eight miles as the height of the meteoric cloud. The 
anomalies, however, in regard to the corresponding 
differences of right ascension, are such, that the 
change of apparent position in the heavens in ad- 
vancing from north to south might have been 
owing to some other cause than parallax. We 
also consider this estimate of the distance of the 
meteoric cloud as only an approximation, the best 
that can be derived from data that are imperfect, 
and sometimes discordant, and regard it as proba- 
ble that the real source of the meteors was con- 
siderably more distant than the limit here assigned. 

Material substances comparatively so near the 
earth as two or three thousand miles would be 
strongly affected by the earth's gravity, and bodies 
constituted of exceedingly light materials would be 
readily attracted down to the earth from such a 
height. Gravity, therefore, being both a known 
and an adequate cause, is assigned as the force by 



which the meteors were drawn or impelled towards 
the earth ; and hence it is inferred that they fell in 
parallel lines directed to the centre of the earth. 
This accounts for their apparent radiation from a 
common centre, as will be readily understood from, 
the annexed representation. 




Let ABC represent the vault of the sky, the 
centre of which D being the place of the specta- 
tor. Let 1, 2, 3, &.C., represent parallel lines 
directed towards the earth. A luminous body 
descending through the line D E, coincident with 
the axis of vision, would appear stationary all the 
while at V; a body descending the line marked 
2, 2 would appear to describe the short arc 2', 2'; 
and a body descending the line 3, 3 would appear 
to describe the longer arc 3', 3'. By considering 
thus the manner in which the arcs described on 
the celestial vault would appear, according as the 
meteor was nearer the axis of vision or more re- 
mote from it, we shall arrive at the following con- 
clusions: — that those meteors which fell nearer to 
the axis of vision would seem to describe shorter 
arcs, and move slower, while those which were 
further from the same axis would appear to de- 
scribe longer arcs, and to move Avith greater ve- 
locity ; that the meteors would all seem to radiate 
from a common centre, namely, the point where 
the axis of vision D E met the celestial vault ; 
and that if any meteor chanced to move directly 
in the line of vision, it would be seen as a luminous 
body stationary for a few seconds at the centre of 
radiation. All these conditions are in perfect ac- 
cordance with the appearances of the meteors as 
described by various observers. 



356 



WONDERS OF THE HEAVENS 



Although it is doubtful, from the want of the re- 
quisite data, whether the source of the meteors, or 
the height of the meteoric cloud, has been accu- 
rately ascertained, yet the limit above estimated is 
confidently believed not to exceed the actual dis- 
tance. According to the established laws of falling 
bodies, the inquiry is next instituted, what velocity 
the meteors would acquire in falling from a point 
two thousand two hundred and thirty-eight miles 
above the earth to within fifty miles of its surface, 
this being considered as nearly the height of the 
atmosphere. The calculation gives nearly a veloc- 
ity of four miles per second as that with which the 
meteors entered the earth's atmosphere, a velocity 
more than ten times the maximum velocity of a 
cannon-ball, and about nineteen times that of 
sound. It must be recollected that the atmosphere 
diminishes in density very rapidly as we ascend 
from the earth, until, at the height of fifty miles, it 
is so rare as hardly to oppose the least resistance 
to a body moving in it. It is well known that 
when air is suddenly compressed, a great quantity 
of heat is extricated from it. A little instrument 
is constructed on this principle for lighting tinder, 
by forcing down a solid piston upon a confined 
column of air in a small barrel. A spark is elicit- 
ed, which ignites tinder at the bottom of the barrel. 
In the same manner the meteors, on entering the 
atmosphere, produced a sudden and powerful com- 
pression of the air before them, thus extricating 
heat sufficient to produce in them an intense igni- 
tion, and, if they were combustible, to set them on 
fire. 

The meteors were constituted of very light, 
combustible materials. Their combustibility was 
rendered evident by their exhibiting the actual 
phenomena of combustion, being consumed, or 
converted into smoke, with intense light and heat; 
and the extreme tenuity of the substance composing 
them is inferred from the fact that they were stop- 
ped by the air. Had their quantity of matter been 
considerable, with so prodigious a velocity they 
would have had sufficient momentum to enable 
them to reach the earth, and the most disastrous 
consequences might have followed. Upon submit- 



ting the subject to accurate calculation on estab- 
lished principles, it was ascertained that the quantity 
of heat extricated from the air by the falling mete- 
ors exceeded that of the hottest furnaces, and could 
be compared only to those immeasurable degrees 
of heat produced in the laboratory of the chemist, 
before which the most refractory substances are 
melted, and even dissipated in vapor ; and of course 
it was abundantly adequate to account for all the 
effects of ignition and combustion which were ac- 
tually observed. Mr. Twining, indeed, supposes 
the meteors to have had a relative velocity, arising 
from the earth's motion towards them, independent 
of the motion here supposed to arise from gravity; 
and that they fell towards the earth with a velocity 
of fourteen, instead of four miles per second. 
Should this estimate prove the more correct, it will 
not set aside the conclusions based upon the idea 
of the meteor's falling into the atmosphere with 
very great velocity, but the intensity of the cause, 
and its adequacy to produce the effects ascribed to 
it, will be proportionally augmented. 

Some of the larger meteors must have been bod- 
ies of very large size. If we know the actual 
distance of a luminous body, and its apparent 
diameter compared with that of the moon, it is easy 
to compute its real dimensions. In the present 
case, we have no means of ascertaining the exact 
distance of any meteor from the observer, and can 
only make probable suppositions. Dr. Smith, of 
North Carolina, and other persons in various plac- 
es, saw a meteor which appeared as large as the 
full moon. If this body were at the distance of one 
hundred and ten miles from the observer, it must 
have had a diameter of one mile ; if at the distance 
of eleven miles, its diameter was five hundred and 
twenty-eight feet ; and if only one mile off, it must 
have been forty-eight feet in diameter. These 
considerations leave no doubt that many of the 
meteors were bodies of large size, though it may 
be difficult to say precisely how large. The fact 
that they, were stopped by the resistance of the air, 
proves that they were constituted of very light 
materials ; still the quantity of smoke or residuum 
which resulted from their destruction indicates 



WONDERS OF THE HEAVENS 



357 



that their quantity of matter was considerable. 
The momentum of even light bodies of such size, 
and in such numbers, traversing the atmosphere 
with such astonishing velocity, must have produced 
extensive derangements in the atmospheric equi- 
librium. 

These large bodies were stopped in the atmo- 
sphere only by transferring their motion to columns 
of air, large volumes of which would be suddenly 
and violently displaced. Cold air of the upper re- 
gions would be brought down to the earth; the 
portions of air incumbent over districts of country 
remote from each other, being mutually displaced, 
would exchange places, the air of the warm lati- 
tudes being transferred to colder, and that of cold 
latitudes to warmer regions. Remarkable changes 
of seasons would be the consequence, and numer- 
ous and violent gales would prevail for a long time, 
until the atmosphere should have regained its equi- 
librium. That the state of the weather, and the 
condition of the seasons that followed the meteoric 
shower, corresponded to these consequences of the 
disturbance of the atmospheric equilibrium, is a 
remarkable fact, and favors the opinion that such 
disturbance is a natural effect of the meteoric 
shower, and it is a consequence from which the 
most formidable dangers attending phenomena of 
this kind are to be apprehended. 

Although it is doubtful whether the meteors, in 
any case, reached the ground, yet there is reason 
to believe that they sometimes descended very low. 
A credible witness asserted that he saw one ex- 
plode and leave its train between his eye and an 
opposite precipice several hundred feet in height. 
The remarkable meteor before mentioned as having 
exploded near the star Capella, left a train which 
exhibited appearances so peculiar, that it was a fit 
object upon which to build the inquiry whether the 
same meteor was seen by persons remote from each 
other. If this were the fact, then the different 
points in the heavens to which different observers 
would refer it would furnish data for estimating its 
height. Mr. Twining rendered it probable that 
the fact was so, and grounded upon it the esti- 
mate that the place where the meteor exploded 



was twenty-nine and a half miles above the surface 
of the earth. Circumstances, however, made it 
somewhat doubtful whether any single meteor 
could be identified as seen by different and distant 
observers ; and other facts strongly indicated that 
the place of explosion was much nearer to the 
earth than the limit assigned by Mr. Twining. 

With regard to the nature of the meteors, after 
establishing the fact that they were combustible, 
light, and transparent bodies, it was inferred that the 
cloud which produced the fiery shower consisted 
of nebulous matter, analogous to that which com- 
poses the tails of comets. We do not know, in- 
deed, precisely what is the constitution of the 
material of which the latter are composed ; but we 
know that it is very light, since it exerts no appre- 
ciable force of attraction on the planets, moving 
even among the satellites of Jupiter without dis- 
turbing their motions, although its own motions, in 
such cases, are greatly disturbed, thus proving its 
materiality; and we know that it is exceedingly 
transparent, since the smallest stars are visible 
through it. Hence, so far as we can gather any 
knowledge of the material of the nebulous matter 
of comets, and of the matter composing the meteors 
of November 13th, they appear to be analogous to 
each other. 

Various hypotheses have been proposed to ac- 
count for this wonderful phenomenon. The agent 
which most readily suggests itself in this and in 
most other unexplained natural appearances, is 
electricity. But no known properties of electricity 
are adequate to account for the production of the 
meteors, for the motions that they exhibited, or 
for the trains that they, in many instances, left 
behind them. And if this agent be supposed to 
have some connection with the light and heat which 
they exhibited, it maybe replied, that the compres- 
sion of the air which must result from the rapid 
progress of large bodies through it is a sufficient 
cause of these. Indeed, electricity itself, accord- 
ing to the most rational view, owes its light and 
heat to the same cause. Magnetism has also been 
assigned as the principal agent concerned in pro- 
ducing the meteoric shower. The aurora borealis, 




WONDERS OF THE HEAVENS 



and the remarkable auroral arches which occasion- 
ally appear in the sky, have been found to have 
peculiar relations to the magnetism of the earth, 
arranging themselves in obedience to the laws of 
magnetic attraction. Something of this kind was 
supposed by some to appear during the meteoric 
phenomenon, especially in the position of the ap- 
parent radiant, which was, as noticed by many ob- 
servers, very nearly in the place towards which 
the dipping-needle is directed. From other obser- 
vations, however, it is proved that the radiant point 
was not stationary with respect to the meridian, 
but accompanied the stars in their westerly pro- 
gress, and, of course, that such an apparent coin- 
cidence with the pole of the dipping-needle was 
purely accidental. Moreover, were magnetism 
competent to explain the direction of the meteors, 
it would still leave their production unaccounted for. 
Hydrogen gas, or phosphoretted hydrogen, has 
been alleged as another cause of the meteoric 
shower. Collections of this substance, it has been 
supposed, were exhaled into the higher regions of 
the atmosphere, according to the hypothesis of the 
formation of ignes fatui, and, becoming inflamed, 
exhibited the appearance of falling stars. Electri- 
city has sometimes been called in to aid the entire 
explanation. It is sufficient to say of this hypoth- 
esis, that it is assigning a cause not known to exist, 
and which, if its existence be granted, is not suffi- 
cient to account for the phenomena. According to 
the view that has been taken of the origin of mete- 
oric stones, namely, by ascribing them to terrestrial 
comets, the hypothesis has been suggested, that 
the meteors in question might have a similar origin. 
But the body which afforded the meteoric shower 
could not have been of the nature of a satellite to 
the earth, because it remained so long stationary 
with respect to the earth. The periodical time of 
a satellite revolving in a circle at the distance of 
six thousand one hundred and ninety-four miles 
from the centre of the earth (the estimated distance 
of the body in question) would be two hours forty- 
five minutes and twelve seconds ; and consequently 
its mean motion at the perigee, in a circle, would 
be nearly four miles per second; and its motion in 



an eccentric ellipse at the perigee, would be about 
five and a half miles per second. This result is 
plainly incompatible with the supposition that the 
body in question was a satellite to the earth, since it 
remained stationary with respect to the earth for 
at least two hours, a period sufficient to have it 
carried nearly round the earth in a circular orbit, 
and through many degrees of a parabolic orbit. 

Nor can we suppose that the earth in its annual 
progress came into the vicinity of a nebula, which 
was either stationary, or wandering lawless through 
space. Such a collection of matter could not re- 
main stationary within the solar system, in an in- 
sulated state ; and had it been in motion in any 
other direction than that in which the earth was 
moving, it would soon have been separated from 
the earth, since, during the eight hours while the 
meteoric shower lasted, (and perhaps it lasted 
much longer,) the earth moved in its orbit through 
the space of nearly five hundred and fifty thousand 
miles. 

On projecting a diagram to represent the re- 
spective places of the earth in its orbit, and the 
place of the body which afforded the meteoric 
shower, on the morning of the 13th of November, 
there was exhibited the remarkable fact, that the 
earth, in its annual revolution, was moving almost 
directly towards the point from which the meteors 
proceeded, varying from it but two and one-fourth 
degrees. Now the meteoric cloud remained appa- 
rently at rest, and of course nearly in the earth's 
path, for at least two hours. This it could not 
have done unless it had been moving nearly in the 
same direction as the earth, and with nearly the 
same angular velocity round the sun. For, had it 
been at rest, the earth, moving at the rate of nine- 
teen miles per second, would have overtaken it in 
less than two minutes ; or had it been moving in 
the opposite direction, the meeting would have 
occurred in still less time ; or had not the angular 
velocities of the two bodies been nearly equal, they 
could not have remained so long stationary with 
respect to each other. Hence it was inferred that 
the body which afforded the meteors was pursuing 
its way along with the earth round the sun. 



■rr' ■ ' TM"f Vl-'l W f **""— 



WONDERS OF THE HEAVENS 



Two other conclusions are sustained in the 
Journal of Science. These are, that the body 
revolves around the sun in an elliptical orbit but 
little inclined to the plane of the ecliptic, and hav- 
ing its aphelion near the orbit of the earth. That 
the body has a period of nearly six months, and its 
perihelion a little belov^ the orbit of Mercury. 

A remarkable light was seen in the east at the 
time of the meteoric phenomenon, and subsequent- 
ly in the west after twilight, at different times, until 
the month of May, which light assumed different 
aspects, corresponding, apparently, to those which 
the body revolving around the sun in the manner 
contemplated by the theory would occupy. Hence 
it was conjectured that this luminous appearance 
proceeded from the body itself which afforded the 
meteoric shower. Should future observation estab- 
lish the truth of this conjecture, the fact would 
afford a striking confirmation of the theory; but 
the theory was founded on evidence independent of 
this last consideration. It was also suggested that 
this light might have resulted from the same cause 
as the zodiacal light, and that the latter unexplained 
phenomenon perhaps results from a nebulous body 
revolving around the sun interior to the orbit of the 
earth. 

We must advert, for a moment, to the provident 
care that the Creator displayed in shielding the 
earth from the direful effects which the "fiery 
shower" might, without such care, have unques- 
tionably produced. Had the meteors been consti- 
tuted of materials a little more dense, their 
momentum would have enabled them to reach the 
earth; and had they held on their course three 
seconds longer, it is impossible to conceive of the 
calamities that would have ensued by the descent 
to the earth of bodies of such magnitude, glowing 
with the most intense heat. Half the continent 
might have been involved in one common destruc- 
tion. 

If the above reasonings and conclusions were 
correct, there wsls a chance at least that similar 
phenomena might be again seen in November, 
1834. Such was in reality the case, and the pub- 
lic have been favored with an account of them in 




the Journal from which we have already drawn so 
freely, and to which we again turn for information. 
On the morning of the 13th of November, 1834, 
there was a slight repetition of the meteoric 
shower that presented so remarkable a spectacle a 
year before. The presence of the moon in an ad- 
vanced stage, until nearly four o'clock in the morn- 
ing, permitted only the . larger and more splendid 
meteors to be seen ; it may fairly be supposed that 
many of the smaller and fainter meteors, such as 
constituted last year much the greater part, were 
invisible from this cause merely. The number of 
the meteors, however, was evidently above the 
common average. They began to be visible soon 
after one o'clock, when a fire-ball of unusual size 
and splendor blazed forth in the east. From this 
time they were seen to fall at a pretty uniform rate 
until the light of day was far advanced. From a 
quarter past two until quarter past five, there were 
counted in the eastern view, embracing one-third 
of the visible heavens, one hundred and fifty-five. 
Some meanwhile fell in the south-west, and a few 
in the north-west. To estimate the number that 
fell during the whole night at one thousand, would 
not probably be exceeding the truth. The direc- 
tion of the meteors was more remarkable than 
their number, and afforded evidence of the identity 
of the phenomenon with that of 1833. They ap- 
peared to radiate from a common centre as before, 
and that centre was again in the Lion. It was a 
little to the northward and westward of the place 
it occupied the year before. Then it was near 
Gamma Leonis ; this time it was near the Lion's eye. 
This point was not observed to vary in position for 
three hours, thus corresponding to the conclusions 
drawn before concerning the radiant. The meteors 
generally fell in arcs of great circles, but four were 
observed to a'Scend. One at quarter before four 
shot from near Procyon towards the radiant, and 
three were observed moving with extreme slow- 
ness horizontally from west to east, south of Orion 
and the Little Dog. On the 14th of November, 
1835, meteors were again seen in numbers by 
Herschel at the Cape of Good Hope,, by persons in 
the states of New York, Maryland, North Caroli- 



360 



WONDERS OF THE HEAVENS 



na, and again in 1836 by professor Olmsted, the 
result of whose observations is as follows : — 

"Facts already ascertained leave no doubt of 
the recurrence of ' the meteoric shower ' on the 
morning of the 13th of November. About half 
past three o'clock, observing that the meteors be- 
gan to appear in unusual numbers, I directed my 
attention towards the eastern part of the heavens, 
whence they mostly proceeded, and closely watch- 
ed the stars from the Great Bear on the north to 
the south, embracing in my field of view about 
one-third of the firmament. 

It was soon discovered that nearly all the me- 
teors shot in directions which, on being traced 
back, met in one and the same point, near the 
Lion's Eye. For a quarter of an hour, from half 
past three o'clock, I counted twenty-two meteors, 
of which all but three emanated from the above 
radiant point in Leo. Ten left luminous trains ; 
twelve were without trains ; and the three that did 
not conform to the general direction, moved per- 
ceptibly slower than the others. The greatest 
part shot off" to the right and left of the radiant, a 
majority tending south, towards the heart of Hy- 
dra. The next fifteen minutes afforded but seven 
meteors, and the number gradually declined until 
daylight. 

The exact position of the radiant was near a 
small star forming the apex of a triangle with the 
two bright stars in the face of Leo. Its place was 
therefore very nearly the same as in 1834, differ- 
ing only half a degree in right ascension, and all 
the phenomena very much resembled those observ- 
ed that year, except that they continued for a 
shorter period. 

Although shooting stars occur at various seasons 
of the year, yet these meteoric showers, whether 
they occur on a larger or a smaller scale, are 
marked by several striking peculiarities. The 
meteors are much more frequent than usual, and 
sometimes are exceedingly numerous. A larger 
proportion than common leave luminous trains. 
They mostly seem to radiate from a common cen- 
tre, and for several years past the radiant has been 
in nearly the same part of the heavens, namely, in 



the constellation Leo. It is also remarkable that 
the shower is not only repeated on the same day 
of the year, but arrives at its maximum every- 
where, and at every recurrence, at nearly the same 
hour of the morning, from three to four o'clock. 

By a letter from Springvale, Maine, it appears 
that the display was considerably more splendid at 
that place, the whole number of meteors counted 
from three o'clock to fifteen minutes past six being 
two hundred and fifty-three." 

This subject has not escaped the attention of 
Arago, whose profound knowledge of physics enti- 
tles his opinion to great weight. He has adverted 
to it in a paper, of which there is a translation in 
the Edinburgh Philosophical Journal. He mentions 
observations made in France in November, 1835, 
confirmatory of the periodical occurrence of the 
meteors; rejects the idea of their originating within 
the atmosphere ; and, alluding to the grand display 
of them in America in 1833, says — "It is scarcely 
possible at present to see any other mode of ex- 
plaining the astonishing appearance of these bodies, 
than by supposing that, besides the large planets, 
there move round the sun myriads of small bodies, 
which are not visible except when they penetrate 
into our atmosphere, and there become inflamed ; 
that some of these asteroids move in a certain sense 
in groups, and that others are insulated." 

Again he says — "All these facts tend more and 
more to confirm us in the belief that there exists a 
zone composed of millions of small bodies, whose 
orbits meet the plane of the ecliptic towards the 
point which the earth occupies every year from the 
11th to the 13th of November. It is a new plan- 
etary world just beginning to be revealed to us." 
Arago's idea is, that millions of globules, or small 
parcels of nebulous matter, circulate round the sun 
in a vortex or whirlpool, which crosses the earth's 
path about the middle of November ; and some of 
these, drawn from their course by the earth's attrac- 
tion, take fire when they reach the atmosphere, and 
assume the form of shooting stars. He suggests that 
they should be looked for at the opposite point of the 
ecliptic about the end of April, and alludes to an 
observation of Messier, who saw, in June, 1777, at 



WONDERS OF THE HEAVENS. 



361 



mid-day, ^^ a prodigious number of black globules pass 
across the sun for about five minutes." Might not 
these be asteroids ? This hypothesis explains the 
facts better than professor Olmsted's ; for we may 
suppose millions of these small nebulous bodies re- 
volving at all distances and angles round the sun, 
but distributed unequally; some moving singly, 
some in groups or circular trains, and coming in 
contact with the earth at any point of its orbit, less 
or more frequently, less or more abundant, in that 
part of space through which it is moving at the 
time. We would thus account for the occasional 
appearance of falling stars at all seasons of the 
year. The old notion that they were trains of 
hydrogen or some other combustible gas existing in 
the atmosphere, and accidentally inflamed, is found 
to be untenable. 

IGNE S FATUI. 

Those luminous appearances which are popularly 
called "Will-o'-the-wisps" and " Jack-a-lanterns " 
have been alike the object of vulgar superstition 
and philosophical curiosity; and notwithstanding 
all attempts to apprehend and subject them to ex- 
amination, they are not much better understood 
now than they were centuries ago. They are still 
but an ignis fatuus to the philosopher, and a mys- 
tery to the credulous. Probably this light is often- 
er visible than we might be led to imagine, in con- 
sequence of its not being always distinguishable 
from the lights in surrounding houses. These 
mysterious luminaries have been often seen by the 
fishermen on the Connecticut River while they 
plied their nets at night. They commonly stated 
that they saw them a little above the surface of the 
meadow, dancing up and down, or gliding quietly 
along in a horizontal line. Sometimes two, or even 
three, would be seen together, skipping and danc- 
ing, or sailing away in concert, as if rejoicing in 
companionship. A person, returning from abroad 
late in the evening, had to cross a strip of marsh. 
As he approached the causeway, he noticed a light 
toward the opposite end, which he supposed to be 
a lantern in the hand of some person whom he was 

about to meet. It proved, however, to be a soli- 

46 



tary flame a few inches above the marsh, at a short 
distance from the edge of the causeway. He stop- 
ped some time to look at it. It was evidently a 
vapor (phosphoretted hydrogen probably) issuing 
from the mud, and becoming luminous by contact 
with the air. It exhibited a flickering appearance 
like that of a candle expiring in its socket ; alter- 
nately burning with a large flame, and then sinking 
to a small taper, and occasionally for a moment 
becoming quite extinct. It remained constantly 
over the same spot. 

These lights have been supposed endowed with 
a locomotive power. They appear to recede from 
or advance toward the spectator. This appearance, 
however, may be explained without attributing to 
them any change of distance, but by supposing a 
change in respect to the quantity of flame. When 
the light dwindled, it would appear as if it receded, 
and with a velocity proportioned to the rapidity of 
its diminution. As it became larger, it would seem 
to be advancing toward the spectator. When it 
expired, by several flickerings or flashes, it would 
seem to skip from him ; and when it reappeared, he 
would easily imagine that it had assumed a new 
position. This reasoning will account for their 
apparent motion to or from the spectator. Do they 
ever move in any other direction — in a line per- 
pendicular or oblique to that in which they first 
appeared? In one instance a close observer 
thought this was so, and the light, singularly 
enough, seemed to move directly against a strong 
wind with great rapidity. After gazing for some 
time, he reflected that he had not changed the 
direction of his eye at all, but if the apparent mo- 
tion had been real, he must have turned half 
round. The deception was occasioned by the mo- 
tion of the wind itself — as a stake standing in a 
rapid stream will appear to be moving against the 
current. 

It is a common notion that the ignis fatuus can- 
not be approached, but moves off" as rapidly as we 
approach it. This must be an illusion. Persons 
attempting to approach them have been probably 
deceived as to their distance, and, finding them 
farther off" than they had imagined, have given over 



iJ 



362 



WONDERS OF THE HEAVENS 



the attempt, under the impression that the pursuit 
was vain. A man who said that "he actually stole 
up to one" and thought he had caught it in his hat, 
was asked, " and what was it ? " "It was nothing." 
On looking in his hat for the shining jelly, it had 
wholly disappeared. His motions had dissipated 
the vapor, or his foot had closed the orifice fi-om 
which it issued. The circumstance of these 
lights appearing usually over marshy ground, ex- 
plains the popular notion that they possess the 
power of beguiling persons into swamps and fens. 
In a misty night they are easily mistaken for the 
light of a candle in a neighboring house, and the 
traveller, directing his steps towards it, meets with 
fences, ditches, and other obstacles; and, if he 
perseveres, he soon is quite bewildered in the mid- 
dle of the swamp itself By this time he begins to 
find out that the light is but a "will-o'-the-wisp." 
A man left his neighbor's house late in the even- 
ing, and at daylight had not reached his own, a 
quarter of a mile distant. Accordingly a number 
of persons went in search of him. They found 
him near a swamp, with soiled garments and a 
thoughtful countenance, reclining by a fence. He 
stated that he had been led into a swamp by a 
jack-a-lantern. Yet there was nothing marvellous 
in this. The night was dark, and the man's senses 
being a little disordered by a glass of his neigh- 
bor's punch, he saw a light, and supposing it was 
on his own mantel, he made toward it. A bush 
might have led him to the same place, if he had 
mistaken it for his chimney top. 



SECTION IV. 

Aerolites — Their resemblance to each other — A proof of their common 
origin — Direction in which they appear to move — -No theory as to 
their origin satisfactory — Accounts of various aerolites — Their 
specific gravity — The substances of which they consist — They 
could not have been produced in the atmosphere — -Do they fall 
from the moon? — Or, are they fragments of an exploded planet? 

Solid bodies composed of mineral substances have 
been observed to fall from the upper parts of the 



atmosphere, and they have for this reason been 
named aerolites, which means stones of the air. 
The reality of their fall was doubted for a long 
time, and the general belief in their existence vi^as 
regarded as a popular delusion. But their exist- 
ence has been confirmed by such testimony as can 
no longer be resisted. 

Their most remarkable characteristic is that 
they perfectly resemble each other, being all of 
them masses glittering with metallic particles. 
The external surface is black, as if so colored by 
fire ; while the interior is a yellowish white. They 
all have nearly the same specific gravity. The 
substance of which they are composed is for the 
most part metallic; but the ore of which they con- 
sist is not to be found in the same constituent 
proportions in any terrestrial substances. Their 
fall is generally preceded by a luminous appear- 
ance, a hissing noise, and a loud explosion; and 
when found immediately after their descent they 
are always hot. Their size differs, from small frag- 
ments of inconsiderable weight to the most ponder- 
ous masses. Some of the largest portions of these 
stones have been found to weigh from three hundred 
pounds to several tons, and they have often de- 
scended to the earth with a force sufficient to bury 
them many feet under the soil. In some instances 
they have penetrated through the roof of houses 
and proved destructive to the inhabitants. 

Their common character proves beyond a doubt 
that these stones have a common origin. We 
might remark, also, that iron in a metallic state is 
scarcely to be met with in terrestrial bodies. 
Volcanic substances do not contain any which is 
not oxydated. Aerolites also contain nickel, which 
is very rare, and never found at the surface of the 
earth. They contain chrome, which is still more 
rare. These facts make it probable that meteoric 
stones have an origin foreign to our globe, or at 
least that they are not the product of any phenom- 
enon hitherto observed. 

These masses of matter are discharged upon the 
earth by a species of meteors which have been 
named fire-balls. They are in fact burning globes, 
that appear suddenly in the atmosphere, and 



WONDERS OF THE HEAVENS 



363 



move with extreme rapidity. Their velocity is some- 
times equal to that of the earth in its orbit, (or 
one thousand and one hundred miles a minute.) 
They move in a direction inclined to the horizon. 
After shining with great splendor for a few mo- 
ments, they explode with a loud noise, often at a 
great height above the surface of the earth. They 
do not appear to affect any particular direction 
with regard to the earth's motion, but tend toward 
all the various points of the compass. Philosophers 
have in vain attempted to account for the origin of 
the aerolites. No idea has yet been generally 
adopted on this subject. True, two theories have 
been started, but they are of so extraordinary a 
nature as to excite rather our astonishment at the 
novelty and boldness of their conception, than a 
persuasion of their truth. These are, 1st, That 
they originate in the moon, being thrown beyond 
the sphere of its attractive power by volcanoes; 
2d, That they are portions of a planet once existing 
between Mars and Jupiter. We shall give the 
reasoning used in support of each of these theories. 
They will tend, at least, to show how difficult and 
even hopeless is the settlement of such a question. 

The conjecture that these stony masses are from 
the moon, would hardly originate seriously from 
any but an astronomer. An ordinary person might 
at random utter the vague expression of a thing's 
coming from that luminary ; yet none but a philoso- 
pher could propose such a conjecture with any 
hope of proving its possibility. La Place attempt- 
ed to do this by mathematical calculation. He 
showed that if a mass were projected by a volcano 
from the moon with a certain velocity, (about one 
mile and a half per second,) it would be thrown 
beyond the sphere of the moon's, and into the 
confines of the earth's attraction, and consequently 
fall to the earth. To prepare the way for a com- 
parison of the supposed causes with the phenomena 
themselves, it may be well to enter into some 
details of the observed circumstances attending 
their fall. 

Traditions have prevailed in almost all ages, and 
among all people, of the fall of solid materials from 
the atmosphere, under the various denominations 



of thunderbolts, showers of stones, masses of native 
iron, and so forth, generally believed to have 
descended from the sky or heavens, and ascribed to 
the miraculous judgments of the Deity; while they 
were as generally disbelieved by philosophers, 
either because they had never seen the fall, or 
because they found it impossible to account for it. 
Pliny relates that, in the time of Anaxagoras, the 
preceptor of Socrates, a stone fell to the earth in 
the daytime, near the river ^gos, in Thrace, (as 
large as a wagon load) of a burnt color, and at the 
same time that a comet was visible at night. There 
was another stone of the same origin preserved 
in a public place at Abydos, and held in great 
reverence; a third at Cassandria, in Macedonia; 
fourth at Vorantia, 

In later ages of the world the fact has been 
observed so often by respectable evidences, and 
recorded Avith circumstances of such accuracy, that 
there now remains "no loop whereon to hang a 
doubt." One instance of this kind is given by 
Gassendi, a celebrated astronomer, who was an 
eye-witness of what he relates. November 27th, 
1627, the sky being quite clear, he saw a burning 
stone fall on a mountain in the south-eastern ex- 
tremity of France, near the coast of the Mediter- 
ranean. While in the air it seemed to be about 
four feet in diameter ; it was enclosed in a luminous 
circle of colors like a rainbow, and in its fall pro- 
duced a sound like the discharge of cannon. It 
weighed fifty-nine pounds, was very hard, of a dull 
metallic color, and its specific gravity was con- 
siderably more than that of marble. 

Prior to this a stone fell at a town in Alsace, in 
the north-eastern part of France, near the upper 
Rhine. This was in 1492, November 7th, between 
eleven and twelve before noon, when a dreadful 
thunder-clap was heard at that place, and a huge 
stone seen to fall on a field lately sown with wheat. 
On the people going to the place, a hole was found, 
and digging out the stone, they perceived that it 
had penetrated to the depth of three feet. The 
stone weighed two hundred and sixty pounds ; its 
size, therefore, was equal to a cube of thirteen 
inches the side. No doubt was entertained of this 



364 



WONDERS OF THE HEAVENS 



fact; cotemporary writers agree in its general 
belief by the neighborhood, and the natives of the 
place must have know^n if such a hole or stone had 
before existed in that wheat-field. In 1672, two 
stones fell near Verona, in Italy, the one weighing 
three hundred, the other two hundred pounds. 
Soon after, a member of the Abbe Bourdelot's 
academy presented, at one of their meetings, a 
specimen of these two stones ; stating that the phe- 
nomenon had been seen by three or four hundred 
persons ; that the stones fell in a sloping direction, 
during the night and in calm weather ; that they 
appeared to burn ; that they fell with great noise, 
and ploughed up the ground. It is related by Paul 
Lucas, the traveller, that when he was at Larissa, in 
Greece, a stone fell in the neighborhood weighing 
seventy-two pounds. It was observed to come 
from the northward with a loud hissing noise, and 
seemed to be enveloped in a small cloud that 
exploded when the stone fell. It looked like iron 
dross, and smelled of sulphur. In September, 
1753, several stones fell, accompanied with loud 
noises, a little west of Geneva, two of them falling 
within nine miles of each other. The sky was clear 
and the weather warm. A loud noise and hissing 
sound were heard for many miles round. The 
stones appeared exactly similar to each other, of a 
darkish, dull color, very heavy, and their surface 
appearing as if they had suffered a violent degree 
of heat. The largest weighed about twenty pounds, 
and penetrated about six inches into the ploughed 
ground. This phenomenon has been described by 
La Lande, the astronomer, who seems to have 
carefully examined, on the spot, the truth of the 
circumstances he describes. 

In the year 1768, there were presented to the 
academy of sciences at Paris three stones which 
had fallen in different parts of France ; one in the 
Maine, another in Artois, and the third in Cotentin. 
These were externally of precisely the same ap- 
pearance. On the first of them a report was made 
by a select committee, who stated that on the 18th 
of September, between four and five o'clock, P. M., 
there was seen, near the village of Luce in Le 
Maine, a cloud, in which a short explosion took 



place, followed by a hissing noise, but without any 
flame ; that some persons about ten miles from 
Luce heard the same sound, and looking upward, 
perceived an opaque body describing a curve line 
in the air, and fall on a piece of green turf near 
the high road ; that they immediately ran to the 
spot, and found a stone half buried in the earth, 
extremely hot, and weighing seven and a half 
pounds. In his account of a shower of small stones 
which fell at Guienne, in the south-western part of 
France, on the 24th of July, 1790, D'Arcet men- 
tions two singular circumstances as coming directly 
under his own observation : viz. that the stones, 
when they fell on the houses, had not the sound 
of hard and compact substances, but of matter in a 
soft, half-melted state; and that such of them as 
fell upon straws, adhered to them so as not to be 
easily separated. December 19th, 1798, at eight 
o'clock in the evening, a large fire-ball was seen 
at Benares, in Bengal : it was attended with a loud 
rumbling noise. The inhabitants of Krakhut, four- 
teen miles from Benares, saw the light, heard a 
sound like a loud thunder-clap, and immediately 
after, a noise as of heavy bodies falling to the 
earth. The watchman of an English resident 
brought him, the next morning, a stone that had 
fallen through the top of his hut and buried itself 
in the earthen floor. During the explosion of a 
fire-ball near Bordeaux, in 1789, a stone fell 
through the roof of a cottage and killed a herdsman. 
An aerolite fell at Nobleboro', Maine, on the 7th 
of August, 1823, between four and five o'clock, 
P. M. The account was given by a person at 
work near the spot. His attention was attracted 
by a noise which at first resembled platoon firing, 
but soon became more rapid in succession. The 
air was calm and the sky clear, with the exception 
of a small white cloud, apparently about forty feet 
square, nearly in his zenith: from this the sound 
seemed to proceed. After the explosion this cloud 
appeared to be in a rapid spiral motion downward, 
as if about to fall on him, and it made a noise like 
a whirlwind among the leaves. At this moment a 
stone fell among some sheep, that were much 
frightened, and ran off to the woods. This circum- 



WONDERS OF THE HEAVENS 



365 



stance assisted him in finding the spot where the 
stone struck, which was about forty paces in front 
of the place where he was standing. The aerolite 
penetrated the earth about six inches, and there 
meeting a stone, it was broken into fragments. 
When first taken up, which was about an hour after 
its fall, it exhaled a strong sulphureous odor. The 
whole mass, previous to its fracture, probably weigh- 
ed between four and six pounds. Other fragments 
of the same aerolite are said to have been found 
several miles from Nobleboro'. 

On the 10th of February, 1825, an aerolite fell 
at Nanjemoy, Maryland. About noon the people 
were alarmed by an explosion in the air, which 
was succeeded by a loud v»^hizzing noise, (like that 
of a current of air through a small aperture,) that 
seemed advancing nearly parallel with the river 
Potomac in a south-easterly course. Shortly after, 
a portion of ground was found that had been recent- 
ly broken, and on examination a rough stone of an 
oblong shape, weighing sixteen pounds and seven 
ounces, was found about eighteen inches under the 
surface. The stone when taken from the ground, 
about half an hour after it fell, was sensibly warm, 
and had a strong sulphureous smell. It had a hard 
vitreous surface, and when broken appeared to be 
composed of an earthy matrix containing numerous 
globules of various sizes, of a brown color and very 
hard, together with small portions of brownish 
yellow pyrites, which became dark-colored on 
being reduced to powder. Various ideas were 
entertained by the people on finding this stone. 
Some supposed it propelled from a quarry eight or 
ten miles distant ; while others were so fully con- 
vinced that it was thrown by a mortar fi-om a 
packet lying in the river, that they proposed 
manning a boat to take vengeance on her captain 
and crew. Yet all agreed that the noise seemed 
directly over their heads. One gentleman, living 
twenty-five miles from the place where the stone 
fell, said that it caused his whole plantation to 
shake, and that many supposed there had been an 
earthquake. There was no fire-ball or light seen 
in the heavens, and no peculiar smell in the air 
was noticed. An examination of a fragment of 



this stone is detailed in "The Journal of Science," 
from which we extr'act the following. The frag- 
ment weighed four pounds and five ounces. Its 
dimensions were seven by three or four inches ; its 
form an irregular oval, nearly flat where it was 
detached from the larger mass, and bounded by 
irregular curves in the other parts of its surface. 
It is covered, except where broken, by the usual 
black vitreous coating, which in this case has more 
lustre than common. This coating has innumerable 
cracks running in every direction, and communi- 
cating with each other so as to divide the surface 
into portions resembling honey-comb or madrepore, 
and no undivided portion exceeds half an inch in 
diameter. This circumstance seemed to have 
arisen from the rapid cooling of the external vitre- 
ous crust after intense ignition. No one who saw 
this crust could doubt this to be the cause. It is 
not quite so thick as the back of a common pen- 
knife, and is separated by a well-defined line from 
the mass of the stone beneath. On the fractured 
surface the stone is of a light ash gray, or perhaps 
more properly of a grayish white ; it is very uniform 
in its appearance, not being marked with any 
strong contrast of dark and light gray spots. The 
fractured surface of the stone is uneven and granu- 
lar, harsh and dry to the touch, and it scratches 
window-glass, though not with much energy. To 
the naked eye it presents very small glittering 
metallic points, and a few minute globular bodies 
scattered here and there through the mass. With 
a magnifier these appearances are of course much 
increased. The adhesion is so feeble that it falls 
to pieces with a slight blow, and exhibits an 
appearance like grains of sand. The Maryland 
aerolite is highly magnetic, pieces as large as peas 
being readily lifted by the magnet. The iron is 
metallic and perfectly malleable. In the crust the 
iron is glazed over so that the eye does not per- 
ceive its metallic character, but the file instantly 
exposes the innumerable points, which then break 
through the varnish of the crust and give it a bril- 
liant metallic lustre at all the parts where the file 
has uncovered the iron. The specific gravity of 
the specimen was 3.66. On analysis it was found 



366 



WONDERS OF THE HEAVENS 



to contain silica, magnesia, lime, oxide of iron, 
oxide of nickel, sulphur, alumine. 

Several of the preceding accounts notice the 
material circumstance of damage done to objects 
above the ground by these stones. It seems im- 
possible to deny very great weight to all these 
testimonies, and many others that might have been 
detailed, all concurring in the descriptions as near- 
ly as different persons can be expected to do even 
in describing one and the same occurrence. We 
shall notice the main points that seem to be sub- 
stantiated by all witnesses. In various parts of the 
world luminous meteors have been seen moving 
through the air with a noise like the whizzing of 
large shot, followed by explosion, and the fall of 
hard, stony or semimetallic masses in a heated 
state. The constant whizzing sound; the fact of 
stones being found similar to each other, but unlike 
all others in the neighborhood, at the spots toward 
which the luminous body or its fragments were 
seen to move; the scattering or ploughing up of 
the soil at those spots, always in proportion to the 
size of the stones ; the concussion of the neighbor- 
ing ground at the time, and especially the striking 
of the stones on bodies above the earth, or lying 
loosely on its surface, are circumstances perfectly 
well authenticated, proving that such meteors are 
usually inflamed, hard masses, descending through 
the air. 

The reports of all those persons who have seen 
and observed such meteors and found the stones, 
uniformly agree in describing those substances as 
different from all the neighboring bodies, and as 
presenting the external appearance of semimetallic 
matter, coated with a thin black crust, and bearing 
strong marks of recent fusion. Besides this general 
resemblance, obvious to the most careless inspec- 
tion, many of these substances have been carefully 
examined by the first chemists and naturalists, and 
their investigations have put us in possession of 
information sufficient to convince the most sceptical 
that the bodies in question have a common origin, 
and that we are unacquainted with any natural 
process by which they could have been formed on 
our globe. The specific gravities of all these 



aerolites are nearly the same, being between three 
and four, that of water being represented by one. 
In this respect they exceed all the ordinary stones 
of our globe, and approach to those of the metallic 
ores. All these stones that have been examined 
consist of four distinct substances, viz. small metal- 
lic particles, a peculiar pyrites, a number of globu- 
lar and elliptical bodies of a peculiar nature, and 
an earthy cement surrounding the other compo- 
nent parts. The nature of the metallic particles 
is the same in all, being an alloy of iron and nickel. 
The globules contain silica, magnesia, and oxides 
of nickel and iron. The earthy cement consisted 
of the same substances, very nearly in the same 
proportions. We may conclude, then, that the 
substances that have at different times fallen to the 
earth in Europe, India, and America, are exactly 
of the same nature, consisting of the same simple 
substances in nearly the same proportions, and 
forming a heterogeneous compound whose general 
resemblance is complete. The examination of 
native masses of iron found in South America, in 
Siberia, in Bohemia, and indeed in all parts of the 
earth, lead to the conclusion that they are of the 
same origin as those that we denominate aerolites. 
Concerning the Siberian iron there exists a tradi- 
tion among the Tartars that it formerly fell from 
heaven. The fall of a similar body in India is sup- 
ported by the testimony of the emperor Tchangine 
in his memoirs of his own reign. He relates that, 
in the year 1620 of our era, a violent explosion 
was heard at a village in the Punjab, and a lumi- 
nous body fell through the air to the earth. The 
officer of the district immediately repaired to the 
spot where it was said the body had fallen, and 
finding the place hot, he caused it to be dug, on 
which the heat was found to increase till they 
reached a lump of iron violently hot. The emperor 
ordered the mass to be forged into a sabre, a knife, 
and a dagger. The workmen, after trial, reported 
that it was not malleable, but that it shivered 
under the hammer. The mass, however, made 
excellent blades after mixing with it a third part 
of common iron. The exact resemblance of this 
occurrence in its essential circumstances to other 



WONDERS OF THE HEAVENS 



367 



accounts of fallen stones, and the remark on the 
want of malleability in the iron, give a high degree 
of credibility to the whole narrative, and throw 
additional weight on the inference before drawn 
from internal evidence, that the masses of native 
iron found in different parts of the world have the 
same origin as the meteoric stones. From the 
facts and evidence of which a summary has been 
given, may we not safely conclude that the bodies 
in question have fallen to the surface of the earth, 
that they were not projected by any terrestrial 
volcano, and that we have no reason, from the 
known laws of nature, to suppose that they were 
formed in the upper regions of the atmosphere? 
Such a negative conclusion, in the present state of 
our knowledge, seems to be all we are entitled to 
draw. In this embarrassing predicament, some 
persons have come to the conclusion that they 
must have dropped from the moon. As the attrac- 
tion of gravitation extends through the whole plan- 
etary system, a body placed at the surface of the 
moon is affected chiefly by two forces, one drawing 
it toward the centre of the earth, and the other 
drawing it toward the centre of the moon. The 
latter, near the moon's surface, is incomparably the 
greater. But as we recede from the moon, and 
approach toward the earth, this force decreases, 
while the other augments, till at length a point is 
found between the two planets where these forces 
are exactly equal, so that a body placed there 
must remain at rest ; but if removed still nearer to 
the earth, this planet would have the superior at- 
traction, and the body must fall towards it. If, 
therefore, a body be projected from the moon to- 
ward the earth with a force sufficient to carry it 
beyond this point of equal attraction, it must neces- 
sarily fall to the earth. Now, supposing a mass to 
be projected from the moon by a volcano, or by the 
production of steam, owing to the internal heat of 
that satellite, in a direct line toward the earth; 
and supposing the two planets to remain at rest ; it 
has been demonstrated on the Newtonian estima- 
tion of the moon's mass, that a force projecting the 
body with a velocity of twelve thousand feet per 
second, would be sufficient to carry it beyond the 



point of equal attraction. This estimate of the 
moon's mass is now allowed to be much above the 
truth ; and on the calculation of La Place, it ap- 
pears that a force of little more than half the above 
power would be sufficient to produce the effect, 
that is, a force capable of projecting a body with a 
velocity of less than a mile and a half per second. 
A force equal to this is exerted by terrestrial vol- 
canoes ; and we may suppose such a cause of mo- 
tion to exist in the moon, and even in a superior 
degree, from the volcanoes thought to have been 
discovered by Dr. Herschel, especially if we con- 
sider the moon's atmosphere to be very rare or 
limited in extent. 

All the phenomena of aerolites, say the advo- 
cates of their lunar origin, agree well with the 
circumstances of a substance projected from the 
moon. With respect to the bright spark, first seen 
at an immense distance, and gradually increasing 
with the diminution of its distance; — the body, 
being projected from a lunar volcano, may be 
supposed in an ignited state, and, passing through 
the comparative vacuum between the earth's and 
moon's atmospheres, would enter the upper part of 
our atmosphere with but little diminution of its 
original heat; from which circumstance, united 
with its rapid motion, the body may become sud- 
denly inflamed. 

Next, to trace the body through the earth's at- 
mosphere ; — we may observe that it enters the top 
of it with a great velocity, that acquired by de- 
scending from the point of equal attraction, which 
is such as would carry it to the earth's surface in a 
few seconds if it meet with no obstruction. But 
as it enters deeper into our atmosphere, it meets 
with increasing resistance from the density of the 
air, by which its great velocity must be diminished. 
This remaining velocity will be different, according 
to the size and specific gravity of the body; but, 
for a particular instance, if the body were a globe 
of twelve inches diameter, and of the same gravity 
as the aerolites, the motion would be decreased 
from six miles per second to a little more than a 
quarter of a mile per second of perpendicular de- 
scent. Now while the body is thus descending, 



368 



WONDERS OF THE HEAVENS 



the earth is affected by a twofold motion, the diur- 
nal and the annual, with both of which the descent 
of the body is to be compounded. The daily mo- 
tion at the equator is about two-sevenths of a mile 
per second, but in middle latitudes a little more 
than half a quarter of a mile per second. This 
may cause the body to appear to descend some- 
what, though not very, obliquely. But the earth's 
annual motion is about nineteen miles per second ; 
and if this be compounded with the descending 
motion of the body, it will necessarily have the 
appearance of a rapid motion but little declining 
from the horizontal. 

Again, with regard to the apparent direction of 
the body, this will be various, for the motion of the 
earth in its orbit is various at different seasons of 
the year. Usually, however, from the great excess 
of the earth's motion above that of the falling body, 
the direction of the latter must appear nearly op- 
posite to that of the former. 

In the flight of these aerolites, they commonly 
make a loud whizzing sound. And if such a sound 
be given by the smooth round cannon-ball, how 
exceedingly great should be that of a body so much 
larger, and whose form and surface is so irregular. 

These substances commonly burst and fly in 
pieces in their rapid flight — a circumstance that 
might be expected, both on account of the violent 
state of fusion on their surfaces, and from the ex- 
treme rapidity of their motion. That the stones, 
striking the ground with great force, should pene- 
trate to some depth, is not unnatural, since even a 
cannon-ball or a mortar-shell will often bury itself 
in the soil. 

That the stones are hot when found, and exhibit 
signs of recent fusion, is not strange, after the ex- 
treme degree of inflammation to which they are 
subjected in their flight through the air. 

These masses have all the same external appear- 
ance and texture, as well as internally the same 
nature and composition. These are circumstances 
which strongly point to an identity of origin ; and 
their entire want of similarity to any terrestrial 
composition leads the mind to conclude that they 
did not originate on our globe. These are the ar- 



guments that are used to prove the descent of aero- 
lites from the moon. But they prove any other 
origin (apart from a terrestrial one) just as well. 

The existence of four planets between the orbits 
of Mars and Jupiter, revolving round the sun at 
nearly the same distances, and differing from all 
the other planets in their diminutive size, and in the 
form and position of their orbits, is one of the most 
singular phenomena in the history of astronomy. 

The incompatibility of these phenomena with the 
regularity of the planetary distances, and with the 
general harmony of the system, naturally suggests 
the opinion that the inequalities in this part of the 
system were produced by some great convulsion, 
and that the four planets are the fragments of a 
large celestial body which once existed between 
Mars and Jupiter. If we suppose these bodies to 
be independent planets, as they must be if they did 
not originally form one, their diminutive size, the 
great eccentricity and inclination to their orbits, 
and their numerous intersections when projected 
on the plane of the ecliptic, are phenomena abso- 
lutely inexplicable on every principle of science, 
and completely subversive of that harmony and 
order which, before the discovery of these bodies, 
pervaded the planetary system. But if we admit 
the hypothesis that these planets are the remains 
of a larger body, which circulated round the sun 
nearly in the orbit of the greatest fragment, the 
system returns to order, and we discover a regular 
progression in the distances of the planets, and a 
general harmony in the form and position of their 
orbits. To a mind capable of feeling the force of 
analogy, this argument must have no small degree 
of weight, and might be reckoned a sufficient 
foundation for a philosophical theory. We are 
fortunately, however, not left to the guidance 
merely of analogical reasoning. The elements of 
the new planets furnish us with several direct ar- 
guments, drawn from the eccentricity and inclina- 
tion of their orbits, and from the position of their 
perihelia and nodes, and all concurring to show 
that the four new planets have diverged from one 
point of space, and have, therefore, been originally 
combined in a larger body. 



WONDERS OF THE HEAVENS 



369 



To those who are acquainted with physical as- 
-tronomy, it is needless to state the difficulty of 
ascertaining the paths of four bodies whose masses 
are known, and which have diverged from one 
common node, with velocities given, in quantity 
and direction. This problem is much more per- 
plexing than the celebrated problem of "the three 
round bodies," and is therefore beyond the grasp 
of the most refined analysis. It is not difficult, 
however, to ascertain in general the consequences 
that would arise from the bursting of a planet, and 
to determine, within certain limits, the form and 
position of the orbits in which the larger fragments 
would revolve round the sun. 

When the planet is rent asunder by some inter- 
nal force capable of overcoming the mutual attrac- 
tion of the fragments, it is obvious that the larger 
fragments will receive the least impetus from the 
explosive force, and will, therefore, circulate in an 
orbit deviating less than any other of the fragments 
from the original path of the large planet ; while 
the lesser fragments, being thrown off with greater 
velocity, will revolve in orbits more eccentric, and 
more inclined to the ecliptic. Now the eccentrici- 
ty of Ceres and Vesta is nearly one-twelfth of their 
mean distances, that of Ceres being rather the 
greatest ; and the eccentricity of Pallas and Juno 
is one-fourth of their mean distances, the eccentri- 
city of Pallas being a little greater than that of 
Juno. We should therefore expect, from the the- 
ory, that Pallas and Juno would be considerably 
smaller than Ceres and Vesta, and that Ceres 
should be the larger fragment, and have an orbit 
more analogous in eccentricity and inclination than 
that of any of the smaller fragments to the other 
planets of the system. In so far as the diameters 
of the new planets have been measured, the theory 
is most strikingly confirmed by observation. The 
observations of Schroeter make Juno considerably 
less than Ceres ; and though the diameter of Vesta 
has not been accurately ascertained, yet the inten- 
sity of its light, and the circumstance of its being 
distinctly visible to the naked eye, are strong proofs 
that it exceeds in magnitude both Pallas and Juno. 

The striking resemblance between the two lesser 

■ 47 



fragments, Pallas and Juno, in their magnitudes, 
and in the extreme eccentricity of their orbits, 
would lead us to anticipate similar resemblances in 
the position of their nodes, in the place of their 
perihelia, and in the inclination of their orbits ; 
while the elements of Ceres and Vesta should ex- 
hibit similar coincidences. Now the inclination of 
Ceres is ten degrees, and that of Vesta seven de- 
grees, while the inclination of Juno is twenty-one 
degrees, and that of Pallas thirty-four degrees ; 
and the two greater fragments having nearly the 
same inclination, and keeping near the ecliptic, 
while the lesser fragments diverge from the original 
path, and rise to a great height above the ecliptic, 
and far above the orbits of all the other planets in 
the system. If it shall be found from observation 
that Vesta is one of the smaller fragments, we may 
then account for its position with regard to Ceres, 
and for the small inclination and eccentricity of its 
orbit, by supposing the planets Ceres, Pallas, and 
Juno to have diverged in the same plane, and 
nearly at right angles to the ecliptic, while Vesta 
diverged from the direction of the original planet 
in a plane parallel with the ecliptic. This opinion 
is strongly confirmed by the fact that the orbit of 
Vesta is nearer to the sun than any of the orbits of 
the other three fragments. 

In the position of the nodes we perceive the 
same coincidence. The orbits of Pallas and Juno 
cut the ecliptic in the same point, and the nodes of 
Ceres and Vesta are not far distant. 

If all the fragments of the original planet had, 
after the explosion, been attracted to the larger 
fragment, it is obvious that they would all move in 
the same orbit, and consequently have the same 
perihelion. If the fragments received a slight de- 
gree of divergency from the explosive force, and 
moved in separate orbits, the points of their peri- 
helion would not coincide, and their separation 
would increase with the divergency of the frag- 
ments. But since all the fragments partook of the 
motion of the primitive planet, the angle of diverg- 
ency could never be very great ; and therefore we 
should expect that all the perihelia of the new 
planets would be in the same quarter of the heav- 



370 



WONDERS OF THE HEAVENS 



ens. This theoretic deduction is most wonderfully 
confirmed by observation. All the perihelia are in 
the same semicircle, and all the aphelia in the 
opposite semicircle ; the perihelia of the two larg- 
er fragments, Ceres and Vesta, being near each 
other, as might have been expected, while there is 
the same proximity between the perihelia of the 
lesser fragments, Pallas and Juno. 

These singular resemblances in the motions of 
the greater fragments, and in those of the lesser 
fragments, and the striking coincidences between 
theory and observation in the eccentricity of their 
orbits, in their inclination to the ecliptic, in the 
position of their nodes, and in the places of their 
perihelia, are phenomena which could not possibly 
result from chance, and which concur to prove, 
with an evidence amounting almost to demonstra- 
tion, that the four new planets have diverged from 
one common node, and have therefore composed a 
single planet. 

Let us now proceed to consider the other phe- 
nomena which might be supposed to accompany this 
great convulsion. When the cohesion of the planet 
was overcome by the action of the explosive force, a 
number of little fragments, detached along with the 
greater masses, would, on account of their small- 
ness, be projected with very great velocity; and 
being thrown beyond the attraction of the larger 
fragments, might fall towards the earth when Mars 
happened to be in the remote part of his orbit. 
The central parts of the original planet being kept 
in a state of high compression by the superincum- 
bent weight, and this compressing force being re- 
moved by the destruction of the body, a number of 
lesser fragments might be detached from the larger 
masses by a force similar to the first. These frag- 
ments will evidently be thrown off with the greatest 
velocity, and will always be separated from those 
parts which formed the central portions of the 
primitive planet. The detached fragments, there- 
fore, which are projected beyond the attraction of 
the larger masses, must always have been torn 
from the central parts of the original body ; and 
it is capable of demonstration that the superficial 
or stratified parts of the planet could never be 



projected from the fragments which they accom- 
pany. 

When the portions which are thus detached 
arrive within the sphere of the earth's attraction, 
they may revolve round that body at different 
distances, and may fall on its surface inconsequence 
of a diminution of their centrifugal force ; or, being 
struck by the electric fluid, they may be precipi- 
tated on the earth, and exhibit all those phenomena 
which usually accompany the descent of meteoric 
stones. Hence we perceive the reason why the 
fall of these bodies is sometimes attended with 
explosions, and sometimes not ; and why they 
generally fall obliquely, and sometimes horizontal- 
ly, a direction which they never could assume if 
they descended from a state of rest in the atmo- 
sphere, or had been projected from volcanoes on 
the surface of the earth. 

If we compare the specific gravity of meteoric 
stones with the density of the new planets, we shall 
obtain another argument in support of the theory. 
It appears from the observations of Maskelyne on 
the attraction of Shehallien, and particularly from 
the experiments of Cavendish on the attraction of 
leaden balls, that the density of the earth increases 
towards its centre ; and therefore the density of the 
central parts must exceed the average density of 
the whole globe. This increase of density no 
doubt arises from the weight of the superincumbent 
mass ; and hence we are entitled to conclude that 
the density of the central parts of every other 
planet is greater than the average density of the 
body. As it is demonstrable, therefore, that the 
fragments of the large planet, which are supposed 
to be meteoric stones, must have been detached 
from the central parts of the primitive planet, the 
specific gravity of meteoric stones ought to exceed 
the average density of the planet. According to 
the observations of Playfair, the density of Shehal- 
lien is only 2.7, while that of the earth is 4.8 ; so 
that the density of the central parts of our globe 
cannot be less than seven or eight, in order to make 
up the mean density. Now the density of the new 
planets, estimated from their position in the system, 
by the method of La Grange, is nearly two; and 



WONDERS OF THE HEAVENS 



371 



reasoning from analogy, and following the propor- 
tion already stated in the case of the earth, we 
should expect that the average density of meteoric 
stones should be between three and four; within 
which limit we may in fact express the specific 
gravity of all of these bodies. This coincidence, 
when taken in connection with the evidence arising 
from the form and position of the orbits of the new 
planets, gives a probability to the theory which no 
other hypothesis can claim. 

It is objected that if meteoric stones are the 
fragments of a planet, why are they all of the same 
kind? If our earth were to be burst in pieces, we 
should find among its fragments stones of every 
description. This objection is founded on the 
supposition that the earth is everywhere stratified, 
and that there exists at its centre the same diver- 
sity of minerals as occur at its surface. This 
opinion is purely hypothetical ; men have scarcely 
penetrated beyond the surface of the globe, and we 
have every reason to believe that the stratification 
is completely superficial. The density of the in- 
ternal mass is known to be extremely great, and 
the magnetism of the earth demonstrates that this 
mass must be either iron-stone, or melted metals, 
which have the magnetic virtue. Now if we sup- 
pose the earth to be burst in pieces by some in- 
ternal force, it is demonstrable that the smaller 
fragments which would be projected beyond its 
sphere of attraction must come from the central 
parts, and that none of the superficial or stratified 
parts would be detached from the fragment to 
which they belong. The only way in w'hich we 
can conceive the superficial parts of the planets to 
be affected, is by the shock given to the fragment 



on which they rest. But this shock cannot produce 
a velocity greater than the velocity of the fragment 
itself; and since that fragment is supposed by the 
hypothesis to continue in an orbit not far from the 
orbit of the original planet, its superficial parts 
must also remain in the same region of the heav- 
ens. The portions of our globe, consequently, 
which would be thrown beyond the reach of its at- 
traction, would be the dense parts towards its 
centre, which probably would be either iron-stone, 
or melted metals, that had the magnetic virtue. 
Reasoning from analogy, therefore, we should draw 
the same conclusion respecting the imaginary plan- 
et between Mars and Jupiter ; and it is a singular 
circumstance, that meteoric stones contain a great 
proportion of iron, that they are endowed with the 
magnetic virtue, and that the large meteoric stones 
which have been found in Siberia and in South 
America are masses of melted iron. 

It would not be diflftcult to anticipate several ob- 
jections that might be urged against the preced- 
ing theory ; but, however formidable these may be, 
we ought to remember that such difficulties do not 
belong to the hypothesis itself, but arise from our 
ignorance of the changes induced upon the frag- 
ments during their passage through the earth's at- 
mosphere, and that they belong equally to every 
hypothesis which has yet been suggested. It is 
not fair, therefore, to demand from one theory an 
explanation of diflSculties which belong to all. It 
is sufficient to give a plausible explanation of the 
phenomena, and to combine under a general prin- 
ciple the scattered facts that cannot otherwise 
be generalized consistently with the established 
laws and analogies of nature. 



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